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Towards a Wiki For Formally Verified Mathematics

An anonymous reader writes "Cameron Freer, an instructor in pure mathematics at MIT, is working on an intriguing project called vdash.org (video from O'Reilly Ignite Boston 4): a math wiki which only allows true theorems to be added! Based on Isabelle, a free-software theorem prover, the wiki will state all of known mathematics in a machine-readable language and verify all theorems for correctness, thus providing a knowledge base for interactive proof assistants. In addition to its benefits for education and research, such a project could reveal undiscovered connections between fields of mathematics, thus advancing some fields with no further work being necessary."

299 comments

  1. Uh ... by David+Gerard · · Score: 2, Insightful

    1. Bertrand Russell's Principia Mathematica got there first.
    2. Godel proved the endeavour was impossible.

    I'm amazed a mathematician proposed this.

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    1. Re:Uh ... by johannesg · · Score: 4, Funny

      So Godel proved that Russell was wrong, then?

    2. Re:Uh ... by Free+the+Cowards · · Score: 5, Informative

      1. Russell did not, as far as I know, write any proofs in machine-readable language.
      2. Goedel proved that such an endeavor cannot contain all true statements. But of course they never claimed that it would.

      Maybe if you paid more attention you would be less amazed.

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    3. Re:Uh ... by RackinFrackin · · Score: 2, Informative

      No. Godel proved that in any axiomatic system there exist statements whose truth values are formally undecidable. If the summary is correct, then this database would contain the whole of known mathematics and use automated theorem proving to do some advances.

    4. Re:Uh ... by PotatoFarmer · · Score: 1

      2. Godel proved the endeavour was impossible.

      You're right. Might as well quit now, since we'll never be able to know everything.

    5. Re:Uh ... by DriedClexler · · Score: 1

      All Goedel proved was that there exist true statements that it can't prove. There are still many theorems it can prove. And the theorems it can't prove are all stuff like, "This statement cannot be proven."

      Show of hands: Who here cares about the software's inability to generate theorems like that? Anyone? Didn't think so.

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    6. Re:Uh ... by caramelcarrot · · Score: 1

      Firstly, those have nothing to do with this. Godel's theorem merely proves that there exists unprovable theorems that are true. In fact, Godel's theorem actually uses the fact that theorems can be verified in finite time - you just go line by line down the proof and check that it uses the axioms appropriately. This is a repository of theorems that are confirmable.

    7. Re:Uh ... by mckinnsb · · Score: 2, Interesting

      No. I'm only a math minor/computer science major, but from my limited understanding on the subject (as it was related to me by one of my smarter professors), Godel showed that Russell's system could not encompass all true statements. The problem (simplistically) lies in what is *demonstrably true* and what is *provably true*. In particular, Godel showed that Russell's system would have problems with things that are demonstrably true, or what you might call "self-evident truths" in philosophy.

      The system proposed however, might find things that are true that people haven't thought about proving yet. I'm sure a mathematician could come along and give a more complete answer.

    8. Re:Uh ... by techno-vampire · · Score: 5, Informative

      I'm no more of a mathematician than you are, but I've had the chance to discuss this with people who really do understand it. Your description is, I think, correct, but not your conclusion. What Goedel proved was not that such an endeavor was impossible, but that it could not be complete. This is because in any system sufficiently advanced to be interesting, there would always be some things that were true but which couldn't be proven to be true. (There would also, BTW, be things that were false but couldn't be shown to be false.)

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    9. Re:Uh ... by Anonymous Coward · · Score: 0

      Actually, I think the incompleteness line of argument here would be to object to this clip (which maybe I am reading wrong):
      "...wiki will state all of known mathematics in a machine-readable language and verify all theorems for correctness, "

      Now, the issue is that this is not guaranteed to possible, correct? Because nobody as of yet has walked around yet and taken the time to reduce every proof to a formal system. In fact, I've never met a mathematician who has done that for any proof, ever. So we have no idea whether or not, in a given system, we have or have not proved informally a theorem that is unprovable in that system formally.

      Unless you restrict "known mathematics" to mean only mathematics that have been formalized so far. Which would be fine, but that's a whole different affair.

      Also, to someone above, I don't think there is any promise that the ONLY unprovable theorems are the weird self-referential ones. We prove that the set of unprovable truths is nonempty via construction of a self-describing theorem, but whether or not there are other members in that set is a different question.

    10. Re:Uh ... by FrangoAssado · · Score: 1

      And the theorems it can't prove are all stuff like, "This statement cannot be proven."

      While that might be true in some sense, that's not the whole story. As an example of an useful such theorem, Matiyasevich (using various people's results) has shown that there's no way to prove if certain Diophantine equations have solutions or not.

      Strictly speaking, all this means is that you can write a Diophantine equation that encodes some statement like the one you stated. But this doesn't detract from the original point: there still exists some Diopnhantine equation for which we can't prove the existence of solutions (or lack thereof) in the set of axioms known as ZFC, and that's interesting in itself.

    11. Re:Uh ... by Anonymous Coward · · Score: 0

      No. Godel proved that in any axiomatic system there exist statements whose truth values are formally undecidable.

      No.

      You forgot the 'sufficiently powerful' part of the theorem.

      It's trivial to construct decidable axiomatic systems and you can even do interesting stuff with them. What you can't do is to represent natural number arithmetic with them.

    12. Re:Uh ... by Free+the+Cowards · · Score: 1

      Any given mathematical fact falls into one of three categories:

      1. Provably true.
      2. Provably false.
      3. Impossible to prove either way.

      All Godel did was prove that category 3 exists. Previously it was thought that all facts fell into either "true" or "false", and the challenge was figuring out which was which.

      You seem to be talking about known mathematics which have not been formalized but are considered to be true. This is, from what I can see, a major target of this wiki. Such things are a major source of uncertainty. Absent a formal proof, maybe there's a faulty piece of reasoning behind it that nobody has found yet.

      Any mathematical fact which has a correct, known proof can be verified by such a wiki, at least in theory (I don't know if the tools are capable yet). Remember that the wiki is not proving facts, it is merely verifying the proofs put in by humans. If the proof is solid then it can be converted to the software's proof language and verified. If there is no such proof then it really shouldn't be considered to be part of known mathematics, since absent such a proof it's not really known whether the statement is true or not.

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    13. Re:Uh ... by zacronos · · Score: 5, Informative

      Very close. To be 100% correct though, Goedel proved that any such endeavor would either be incomplete, or self-contradictory. In other words, for any sufficiently advanced system, there will be some things that are true but which can't be proven to be true within the system, or else there will be some things which can be proven to be true within the system but which can also be proven to be false within the system.

    14. Re:Uh ... by johanatan · · Score: 1

      What does machine-readable have to do with it? Goedel's codification system was the very thing that made his conclusion rock-solid. With actual machines, one would think that the conclusion would be even more forthcoming.

    15. Re:Uh ... by Anonymous Coward · · Score: 0

      1. Russell did not, as far as I know, write any proofs in machine-readable language.
      2. Goedel proved that such an endeavor cannot contain all true statements. But of course they never claimed that it would.

      Maybe if you paid more attention you would be less amazed.

      As far as you know being the operative word(s): russel developed a system of logic which allowed the developement of (he hoped) all of known mathematics.
      In this system, proofs are mathematical and well defined objects and as such can be checked by a computer, though they did not of course exist at the time. The system implemented in Isabelle is actually a (distant) variant of Russel's original system, a brand of type theory.

      As for the second claim, it was in fact a not so implicit assumption that such a system could be sufficient to prove all known mathematical truths, and in the event that it could not, that another more complete system could. Goedel proved both those claims false. In addition, several logicians hoped that these kinds of systems could be proven to be consistent by using other "intuitively consistent" (and weaker) systems of logic. Goedels theorems also robbed them of that pleasure.

      As for Freer's project, it is quite interesting, though it will inevitably have to deal with problems other mathematical knowlege repositories have to deal with, i.e. the disparity of systems, logics and different formalisations (e.g. datatypes used) that are currently used to do formal mathematics.

    16. Re:Uh ... by johanatan · · Score: 1

      And the way he did it was through a formal numbering system for his theorems using prime numbers. Essentially, his system computed a truth statement (i.e., a theorem) such as this (except with an extremely large prime number instead of 1729):

      1729 - - - - - - - - - Well-formed formula no. 1729 is not true

      It's essentially a more formal rendition of the Epimenides Paradox.

    17. Re:Uh ... by Anonymous Coward · · Score: 0

      Partially right...
      Russell didn't write the proofs... leave that to Hilbert to attempt it (not so far removed from the claim in TFA). Godel proved that Hilbert was wrong. Of course, that didn't stop people like Turing who read Godel and promptly said, "Who cares?". Turing showed that it didn't really matter.

      The TFA (yes I read it) is more Turing that Hilbert.

    18. Re:Uh ... by johanatan · · Score: 5, Informative

      My apologies. [I had to brush up on the actual numbering system].

      Correction: The Godel numbering system assigned a unique prime number to each symbol and axiom of his arithmetic. Then, the IDs of the combinations of symbols making up formulas were computed by raising each symbol or axiom ID to the power of its position in the sequence. And, finally, the ID of each proof or theorem by applying the same algorithm to the formula IDs making up each proof. More info here.

    19. Re:Uh ... by SoVeryTired · · Score: 5, Informative

      "Goedel, Escher, Bach" is an absolutely astonishing book about this subject, and the foundations of logic in general. Applications to AI are also discussed. Admittedly, I had to stop reading it since it rather messed my head up (Got about 3/4 through and couldn't stop dreaming about maths). Highly recommended for any self-respecting geek.

      http://en.wikipedia.org/wiki/G%C3%B6del,_Escher,_Bach

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    20. Re:Uh ... by johanatan · · Score: 1

      Yes, but who is to say that known mathematics doesn't already have a contradiction of the sort Godel pointed out? There's a lot of different 'theories' and there's no guarantee that they mesh properly.

    21. Re:Uh ... by lysergic.acid · · Score: 1

      yea, an axiomatic system doesn't have to be complete to be useful. most logical systems we use are incomplete, but their logical consistence still makes them incredibly useful in science, engineering, and even mathematical research. this Wiki won't make mathematical systems complete, but it can still help discover new theorems--and check to see that existing theorems are all logically consistent with each other.

      i mean, if you are working with boolean logic you accept that its fundamental axioms are true. that is simply given when you work with this formal system. its fundamental axioms are not absolutely provable, only provably consistent with one another. but that alone is enough for us to derive great theoretical and practical use from boolean logic--enough for us to be talking to each other over thousands of miles via digital signals processed by complex logic machines.

    22. Re:Uh ... by johanatan · · Score: 1

      While the proof did contain only one such statement which caused the problem, one was enough. Godel did not even attempt to find more because the proof implies that (assuming an infinite amount of knowledge exists) there are infinitely many such statements (obviously one of these infinities has a greater degree than the other in the same way that there are both an infinite number of integers and an [smaller] infinite number of primes).

      In my mind, it's kind of like dividing by zero (everything breaks down at that point). I would imagine it's a little like yeast working through dough.

    23. Re:Uh ... by SoVeryTired · · Score: 1

      Sweet, sweet example of this: the continuum hypothesis. http://en.wikipedia.org/wiki/Continuum_hypothesis

      What this says is that there are "different" sizes of infinity. The "smallest" is that of the integers: -1, 0 , 1, 2 ...

      It is possible to show that one can never pair up every real number with a distinct integer. There are simply "too many" real numbers, and any attempt to pair the two sets up will result in real numbers being left over. In this sense, the set of real numbers is "bigger" than the integers.

      The continuum hypothesis says there is a set bigger than the integers but smaller than the reals. This has been shown to be unproveable (given the normal axioms of set theory, aka Zermelo-frankel set theory). Since it can't be proven or disproven, you can assume it to be either true or false and get consistant, rigorous maths. In a sense, it is both true and false *at the same time*.

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    24. Re:Uh ... by Anonymous Coward · · Score: 0

      All Goedel proved was that there exist true statements that it can't prove. There are still many theorems it can prove. And the theorems it can't prove are all stuff like, "This statement cannot be proven."

      This is completely wrong. It was Russell who identified the kind of self-referential paradox you invoke, and this has very little to do with Godel's conclusions.

      E.g. you can define integers using set theory and some simple axioms. But there are plenty of things that are provably true about integers that you cannot deduce from the axioms. You prove them by using other theories (e.g. group theory) and demonstrating that integers meet your other axioms.

      In other words, if you gave a computer the integer axioms it could deduce a fairly small subset of the things we know about integers. If you gave the computer group theory as well it could deduce some more things. And so on. But where do the new theories come from? Not from a theorem proving machine.

      This point has some interesting philosophical implications about how the brain works. In particular, the brain is not a Turing machine.

    25. Re:Uh ... by Free+the+Cowards · · Score: 2, Informative

      Machine readability is what separates this from Russell's work. In that, by using a machine-readable proof language, the proofs can be verified mechanically.

      Goedel's conclusion is completely irrelevant to this project, so I don't understand why you even discuss it.

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    26. Re:Uh ... by Free+the+Cowards · · Score: 1

      As for the second claim, it was in fact a not so implicit assumption that such a system could be sufficient to prove all known mathematical truths, and in the event that it could not, that another more complete system could. Goedel proved both those claims false.

      What does this even mean? How can a mathematical truth be 'known" if it cannot be proven?

      What Goedel proved false was that it would be impossible to prove all mathematical truths. But working through what is known and creating mechanically-verifiable proofs for all the ones that are actually true is certainly theoretically possible.

      Goedel would be relevant if you were talking about a project to prove every true statement. But we're not, so it's not. I can't understand why anyone would even bring it up.

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    27. Re:Uh ... by Anonymous Coward · · Score: 0

      Well, for one, you mentioned it. (In number 2).

      And, it wasn't so much Godel's conclusion that is of interest, but his method, which was actually only an extension of the method of Hilbert (and to a lesser degree Russell).

      Are you saying that if machines had existed at that time that they could not run the codes? To disprove that assertion if that is what you are saying, then one could simply take the Hilbert system (or the Godel numbering system) and do the computations today starting from known axioms (and in fact, I bet that is exactly what the software in question is doing or going to do). If the numbering system is not identical, then it certainly must be equivalent.

    28. Re:Uh ... by johanatan · · Score: 1

      Reposting as non-AC so you'll be more likely to see this: Well, for one, you mentioned it. (In number 2). And, it wasn't so much Godel's conclusion that is of interest, but his method, which was actually only an extension of the method of Hilbert (and to a lesser degree Russell). Are you saying that if machines had existed at that time that they could not run the codes? To disprove that assertion if that is what you are saying, then one could simply take the Hilbert system (or the Godel numbering system) and do the computations today starting from known axioms (and in fact, I bet that is exactly what the software in question is doing or going to do). If the numbering system is not identical, then it certainly must be equivalent.

    29. Re:Uh ... by orangesquid · · Score: 1

      Of course, I'm wondering if they can import the contents of the Mizar electronic library for tracking the contents of the Journal of Formalized Mathematics (http://www.cs.ualberta.ca/~piotr/Mizar/mirror/http/library/), which would be pretty cool. The big questions are where the wiki and journal both stand on the Axiom of Choice. Some of the corollaries to the axiom of choice that show up in model theory (which has some interesting things to say about the dimension of the real line versus aleph numbers, beta numbers, and omega numbers) have some very odd consequences and can cause problems when trying to create a formal system that relies on the axiom. Reduced forms of the axiom have been proposed that are less prone to paradoxes, but there's a huge body of formal proof work based on the axiom that would have to be re-worked to use a different set of axioms.

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    30. Re:Uh ... by poopdeville · · Score: 1

      What does this even mean? How can a mathematical truth be 'known" if it cannot be proven?

      There is a big difference between truth and provability. Truth is always relative to a structure. But a statement can only be proven (from a set of axioms) if it is true in EVERY structure (that "satisfies" the axioms). This is Godel's completeness theorem.

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    31. Re:Uh ... by Free+the+Cowards · · Score: 1

      I can't tell if you're utterly clueless, or if you're speaking on a level so far above me that I can't even detect the fact that it contains intelligence.

      A statement is either true or false given certain axioms. It's not "relative to a structure" or to anything else outside those axioms. If it is "known" then it has a proof, otherwise it isn't really known.

      All Godel did was prove that there are true statements which have no proof. This is interesting, in that it means it's impossible to mechanically derive all true statements which come from a set of non-trivial axioms. But essentially by definition, any statement which has no proof is not mathematically "known".

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    32. Re:Uh ... by Free+the+Cowards · · Score: 3, Informative

      I only mentioned it because the guy I replied to mentioned it. Points 1 and 2 were separate.

      I do not understand your second paragraph at all. As far as I understand it, this wiki will not be mechanically searching for new, unknown theorems. All it will be doing is mechanically verifying human-created proofs for submitted theorems. For some reason people see machine verification and fly off into nonsense la-la land. But verifying a human-created proof is nothing particularly special. What's interesting about this wiki is only that it aims to build a large-scale repository of theorems and their proofs in a machine-readable language. Nothing about how it works is in any way revolutionary or even all that interesting, only how it's being organized.

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    33. Re:Uh ... by Anonymous Coward · · Score: 0

      (obviously one of these infinities has a greater degree than the other in the same way that there are both an infinite number of integers and an [smaller] infinite number of primes).

      ugh. the integers and primes have the same cardinality.

    34. Re:Uh ... by snarkh · · Score: 3, Informative

      > there will be some things that are true but which can't be proven to be true within the system

      Close but not exactly -- there will be statements P, such that neither P nor (not P) can be proven within the system.
      However, whether such things are not necessarily true or false in themselves.

      For example the continuum hypothesis was shown to be independent of the axioms of the set theory. Therefore, you can add it as an axiom or add its negation as an axiom. It is not true or false in any reasonable sense (although, admittedly most people choose to think of it as being true, whatever that means).

    35. Re:Uh ... by Anonymous Coward · · Score: 0

      Godel proved the endeavour was impossible.

      Really? Goedel proved that all proofs are impossible? I thought he was a logician, not a magician.

    36. Re:Uh ... by johanatan · · Score: 1

      It's relevant because it is possible and even quite likely that we humans already know contradicting theorems (most likely coming from different theories, number, graph, etc.)

      No one has translated all of each of the theories to the others, so we as of the time of this writing do not know if many of the *known* theories will contradict. That's where this system becomes very interesting in the context of Godel. It seems that this system will have to stick to one set of axioms (i.e., one theory) and thus, the natural translation from all known theorems of all other theories must be made just to enter it (and I suspect that this one set of axioms isn't really those of any one 'theory' of math but rather some optimal [from the computer's perspective] set).

      So, whichever of two conflicting theorems is entered first will take precedence over the second and the second (which was entirely valid when working within its original context), will not be allowed to be entered.

    37. Re:Uh ... by johanatan · · Score: 1

      Correction:

      ... thus, the natural translation from all known theorems of all other theories must be made just to enter them ...

      And, to answer how a mathematical truth can be known but not proven:

      I suspect that it is because our 'minds' include something more than just material--something akin to a soul. We can see on a 'meta' level that mere machines cannot.

      See Minds, Machines & Godel

      Also, almost everything else JR Lucas says about Godel is interesting if you're into that kind of thing (and specifically 'reality outruns knowledge' from the 'Implications of Godel's Theorem' essay).

    38. Re:Uh ... by johanatan · · Score: 1

      But, who says that the axioms of set theory are complete or correct (or the only possible set of axioms)? There may be another set of axioms where continuum hypothesis can be proven, no?

    39. Re:Uh ... by johanatan · · Score: 1

      The system must still be able to exhaustively 'check' each new theorem against all pre-existing theorems (and the original set of axioms). The only difference here between a machine that learns new theorems and one that checks theorems is the source of the input. In this case, the input is coming from humans, but it doesn't necessarily have to be so. Both types of machines though I would imagine will use the same algorithm to 'check' the 'inputs' for contradictions with previously known good theorems.

    40. Re:Uh ... by Anonymous Coward · · Score: 0

      http://en.wikipedia.org/wiki/Godel_number <== Link Slashdot won't eat.

    41. Re:Uh ... by SoVeryTired · · Score: 1

      Yes, of course. You could even take the continuum hypothesis, or its negation as an axiom, since it won't contradict the other ones. It's just a really nice illustration of an undecidable problem in an axiomatic system.

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    42. Re:Uh ... by johanatan · · Score: 1

      and check to see that existing theorems are all logically consistent with each other.

      I think it's particularly that part that Godel's theorem will make impossible. Consider the case where a theorem from one view of the world (theory) is inconsistent with a second theorem from another theory which has already been entered. Either the system must reject the second or forget the first. Neither is desirable.

    43. Re:Uh ... by masterzora · · Score: 1

      As the AC said, the integers and the primes have the same cardinality, but you could use the integers and the reals, or the integers and the powerset of the integers or the rationals and the reals or all sorts or many, many, other examples. Just a bad choice with that one, though.

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    44. Re:Uh ... by Free+the+Cowards · · Score: 1

      That's simply false. The system doesn't do anything of the source. When a user provides the system with a theorem, he also provides a proof. So the system only needs to check that proof, and the proof will contain direct references to other theorems that it relies on. There is no need for exhaustive checking or indeed all that many smarts at all.

      To repeat: the wiki doesn't prove submitted theorems, it merely checks the correctness of the human-created proofs submitted with the theorems.

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    45. Re:Uh ... by Free+the+Cowards · · Score: 1

      I suspect that it is because our 'minds' include something more than just material--something akin to a soul. We can see on a 'meta' level that mere machines cannot.

      I'm sorry, but I view this on the same level as I view people who believe that dancing in a certain fashion will make it rain.

      Something is known to be true if there is proof for it. The only place where "soul" enters into things is in choosing the axioms. Everything after that rests on solid logic. If a statement does not have a solid proof then that statement cannot be considered to be true. Some people may choose to abandon logic and believe it to be true with no proof, but that's just people being illogical, not some deep statement that truth exists without proof.

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    46. Re:Uh ... by melikamp · · Score: 4, Informative

      I like the following elementary presentation I picked up from prof. M. Stanley at SJSU:

      A first order axiomatic theory can have any three of the following, but not all four:

      (1) Be recursively axiomatizable, i.e. a computer program can decide the set of axioms.
      (2) Be expressive enough to capture all the basic facts about arithmetic.
      (3) Be consistent, i.e. not allow to derive a contradiction.
      (4) Be complete, i.e. for any statement F, prove either F or (not F).

    47. Re:Uh ... by lysergic.acid · · Score: 1

      well, i meant checking logical consistency within a particular mathematical system, not across different theories. i don't see why the wiki couldn't keep different systems separate. calculus theorems don't have any relevance to axioms of set theory, and vice versa.

    48. Re:Uh ... by logicnazi · · Score: 5, Informative

      I am a mathematician and in fact one who works in this area and what you say is pretty much correct.

      More accurately what Godel showed is that no system complex enough to include arithmetic with a computable proof predicate is complete.

      Let's take this apart and see what it means.

      • Complex enough to include arithmetic: This means the system is complex enough to express standard questions in number theory e.g., for every even number > 2 there are two primes which sum to it and anything else that we can express by quantification over the relation of equality and the operations +, * and exponentiation. I could trivially make a complete consistent system which didn't allow you to express any interesting questions.

        More precisely the system must be sufficiently strong to prove a few basic facts about the integers and not prove false things about the integers.

      • Computable proof predicate: In standard first order logic this simply reduces to the requirement that the axioms in the system must be in principal enumerable by a computer (which is equivalent to saying that there is a sentence in number theory with only a single existential quantifier that can answer whether something is an axiom or not). Without this restriction I could simply declare my system took as axioms all true arithmetical statements. Obviously though to qualify as the sort of mathematics we can verify and check it better satisfy this.
      • consistent: The system doesn't prove both a statement and it's negation.
      • complete: A system is complete if it admits a proof of S or ~S for every statement S in the language of the system. For instance a theory of arithmetic is complete if it proves or disproves every statement built up from basic arithmetic operations (+, *, exponentiation) via logical operations (and, or, not, existential and universal quantification).

      -------------

      People tend to make this whole thing way harder than it is. Here is a quick paragraph long sketch of Godel's first incompletness theorem.

      Suppose there is a predicate P(s,p) which holds whenever p is an integer coding for a proof of the statement coded by the integer s (if you sit down for a few minutes you can figure out how to do the coding). Now suppose that P(s,p) can be expressed by a sentence in number theory involving only an existential quantifier, e.g, P(s,p) Ez(blah holds of s, p) where blah has no quantifiers.

      Now it turns out that if you are a bit clever you can show that there is a sentence G so that

      G holds iff (Ep)P('~G',p)

      Where 'G' denotes the integer that codes for the sentence G. In other words G says "There is a proof that this statement is false".

      Now suppose there was a proof of G. In this case it must follow that since the system correctly interprets arithmetic that there really is a proof of the negation of G. Hence both G and ~G have proofs so the system is incomplete. But if there was a proof of ~G then, as the system correctly interprets arithmetic, there is no proof of ~G. This is a contradiction. So neither G or ~G have a proof.

      ---------

      The only hard part here is showing that G can talk about itself. The formal proof is pretty straightforward if we leave out the details. We define a formula F(n) (where n is a free variable) defined by:

      F(n) n codes for a formula S(x) and (Ep)P('~S(n)',p)

      Now consider the formula F('F'), i.e. apply F to the integer that codes for F. Expanding out the definition we see that

      F('F') (Ep)P('~F('F')',p)

      So we get our G simply by setting G = F('F'). To get an understanding about where you might get the idea to define F as this you need to understand that existential statements are really program and that this is really an application of the recursion theorem.

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    49. Re:Uh ... by logicnazi · · Score: 1

      Crap the post pulled out my double headed arrows since it thought they were markup the last two formula should read

      F(n) iff n codes for a formula S(x) and (Ep)P('~S(n)',p)

      and

      F('F') iff (Ep)P('~F('F')',p)

      --

      If you liked this thought maybe you would find my blog nice too:

    50. Re:Uh ... by logicnazi · · Score: 1

      Godel's theorem tells us that ANY system that provides what we would intuitively call proofs is going to be either incomplete, inconsistent or too weak too be interesting. Godel's theorem applies just as much to the informal output of human mathematicians as it does to computer verified proofs.

      As a working mathematician my goal is always to produce arguments that convey enough information that the reader could turn them into a formal proof with enough time and effort. It would be a huge benefit if we could actually check that we weren't making some dumb mistake when we convince ourselves that we could make the proofs rigorous if we had the time/inclination.

      I highly doubt that mechanical theorem proving is at this point yet. However, I've also long been convinced that one big thing holding it back is the lack of a database of proved theorems. Mathematicians have a huge advantage understanding each other because we all have the same theorems in the back of our heads we learned in school. Computers that are trying to fill in the gaps in our proofs need the same database.

      Moreover, this sort of database will get more mathematicians interested in working on the project as well.

      --

      If you liked this thought maybe you would find my blog nice too:

    51. Re:Uh ... by Anonymous Coward · · Score: 0

      "There's a lot of different 'theories' and there's no guarantee that they mesh properly."

      Sure there is. All of mathematics is consistent with all the rest of it.

    52. Re:Uh ... by johanatan · · Score: 1

      Well, in that case, the system will deterministically (although incomprehensibly to the human mind) exclude some valid corners of the vast universe of knowledge. And, it will depend on which axioms it starts with and which theorems are entered first--they will essentially steer it on a course that's doomed to ignore certain valid pieces of knowledge. That's the limitation of Godel. Of course, the person entering one of these excluded theorems will know that his theorem is correct based on the original axioms of his theory so maybe it will be of interest to see where these collide.

      Nevertheless, I don't think a system which will actually do the sort of verification and discovery of new theorems which I described is all that far off (just ask Ray Kurzweil).

    53. Re:Uh ... by Creepy+Crawler · · Score: 2, Insightful

      Hmm. A lot of footwork to simply explain that there is no grammar in mathematics.

      --
    54. Re:Uh ... by johanatan · · Score: 1

      You should read more philosophy. Materialism isn't the only one out there [and it has serious problems as many thinkers have pointed out]. I would start with JR Lucas if I were you.

    55. Re:Uh ... by johanatan · · Score: 1

      What I would be interested in knowing is if any of our known theorems contradict one another when translated from one valid axiomatic system to another? This is more directly applicable to Godel's work than undecidability, I think. Based on his work, I picture in fact an infinite number of such contradictions (and this may be why quantum mechanics and Newtonian physics do not mesh).

    56. Re:Uh ... by johanatan · · Score: 1

      Mmmm... that's a little bit counterintuitive. It seems obvious to me that there are more integers than there are primes. I suppose cardinality is a bit less precise property than I'd imagined.

    57. Re:Uh ... by Fractal+Dice · · Score: 2, Funny

      You know, Although I've seen it on many shelves (including my own), I'm not sure I've ever met anyone who actually made it all the way through that book. Perhaps its impossible to prove or disprove if it's really a good book.

    58. Re:Uh ... by Ann+Coulter · · Score: 5, Informative

      Godel proved that Peano arithmetic is incomplete. There are some axiomatic systems that are both consistent and complete. Examples of such systems include plane Euclidean geometry and Presburger arithmetic.

      Here are more examples:
      http://en.wikipedia.org/wiki/Complete_theory

    59. Re:Uh ... by Free+the+Cowards · · Score: 1

      You, and everybody else, seem to be giving this system mysterious and powerful properties that it does not possess.

      The system will exclude thoerems which don't carry a correct machine-readable proof. This is not mystical, or very difficult to grasp. You put in a theorem, you put in a proof. If proof is correct, accepted. If proof cannot be verified, fix the proof. If you think the proof is correct but it can't be verified by the system, then either you're wrong, the system is buggy, or you're making fundamentally different assumptions (axioms). Nothing Earth-shaking there.

      --
      If you mod me Overrated, you are admitting that you have no penis.
    60. Re:Uh ... by Free+the+Cowards · · Score: 1

      No thanks. I prefer to stick with what's real. Everything else is just fantasy and delusion. People seem to enjoy it, but it's not for me.

      If you want to talk about unprovable statements that your gut tells you are true, that's fine, but it would be helpful to the discussion if you didn't place them on equal footing with mathematically provable facts.

      --
      If you mod me Overrated, you are admitting that you have no penis.
    61. Re:Uh ... by johanatan · · Score: 1

      I suppose it could keep the different theories separate, but that wouldn't do anything to help us get a holistic view of truth.

      And, I disagree with the 'irrelevance' bit. It was my understanding (and this may just be due to my particular philosophy of mathematics slant--there are different schools of thought on it) that truth is absolute and transcendent. I think that all theorems may be translated from one theory to another (providing that the sets of axioms are sufficiently advanced). The 'truth' is beyond each particular perception of it.

      Therefore, I sort of pictured a system which would collect all of mankind's knowledge in some abstract syntax which could be converted to meaningful contexts (and the conventional 'theories') at will (sort of like the Hilbert approach).

    62. Re:Uh ... by johanatan · · Score: 0, Redundant

      Yea, this system and the system I want are two different entities. The system in question could keep each set of axioms and theories separate and accept the fact that it is essentially shooting a shotgun out into the universe of knowledge. But that isn't as particularly interesting to me as a system which will collect all of scientific knowledge. I think that the points where we see contradictions (i.e., collisions) between theories will provide very useful insight into the nature of our universe. And, it may even be the case that this is exactly the reason that quantum mechanics and Newtonian physics do not mesh.

    63. Re:Uh ... by johanatan · · Score: 1

      Well, what you're missing is that sticking with what's real is just a doomed a process as believing in fantasy. All this means to me is that the universe is greatly mysterious and we cannot know everything, i.e., reality outruns knowledge.

      As long as your content with that, fine. But, for me, that realization raises profound philosophical implications about the nature of humanity and our universe and causes me to seek higher knowledge. I'm not saying that I understand the mystery, I'm just embracing it's existence and engaging it.

    64. Re:Uh ... by Anonymous Coward · · Score: 0

      So in a self contradictory system A xor not A could equal false? A and not A = true? Wouldn't you need a radically different logic base to do anything useful?

    65. Re:Uh ... by louiswins · · Score: 1

      I got all the way through it, I just didn't understand half the stuff that was in it. If I had taken the time to come to terms with each idea as it was presented, I would certainly still be working on it. It's been a couple years, but IIRC, I got about halfway through before everything started going completely over my head.

    66. Re:Uh ... by techno-vampire · · Score: 1

      Thank you for that exposition, although I suspect you went into more detail than the average Slashdotter wanted. From what I gather, basic Arithmetic, with zero, positive integers but no fractions or negative numbers is complex enough if you include infinity.

      --
      Good, inexpensive web hosting
    67. Re:Uh ... by poopdeville · · Score: 1

      I can't tell if you're utterly clueless, or if you're speaking on a level so far above me that I can't even detect the fact that it contains intelligence.

      You're pretty arrogant for being so utterly wrong.

      A statement is either true or false given certain axioms. It's not "relative to a structure" or to anything else outside those axioms. If it is "known" then it has a proof, otherwise it isn't really known.

      No, that is flat out wrong. And Godel certainly proved that a statement is not either true or false given a set of axioms. That doesn't even make sense, though even the most sensible interpretation is wrong. You are butchering the language of modern mathematical logic. Modern mathematical logic is based on Tarskian semantics of truth, in which truth is defined relative to structures.

      Please read a book. http://en.wikipedia.org/wiki/Completeness_theorem is a good start. it begins:

      A first-order formula is called logically valid if it is true in every structure for its language. The completeness theorem shows that if a formula is logically valid then there is a finite deduction (a formal proof) of the formula....
      A more general version of Gödel's completeness theorem holds. It says that for any first-order theory T and any sentence S in the language of the theory, there is a formal deduction of S from T if and only if S is satisfied by every model of T.

      I presented the latter version -- a theory is the set of all sentences deducible from an axiomatization. Note that a model for a theory T is a structure/interpretation (they are synonyms) for which every sentence of T is true.
      http://plato.stanford.edu/entries/modeltheory-fo/ is pretty readable.

      --
      After all, I am strangely colored.
    68. Re:Uh ... by smtrembl · · Score: 1

      You can check out http://marsey.org/ for a natural-language proof very close (in essence) to Goedel's.

    69. Re:Uh ... by Anonymous Coward · · Score: 0

      The Wikipedia article seems to indicate otherwise: "G is not only unprovable but true." So in addition to what you said, there will also be a statement G so that you can add G as an axiom, but not its negation, without making the theory inconsistent.

    70. Re:Uh ... by Ceriel+Nosforit · · Score: 1

      (although, admittedly most people choose to think of it as being true, whatever that means)

      Isn't that the purpose of the axiom of choice? :3

      --
      All rites reversed 2010
    71. Re:Uh ... by caramelcarrot · · Score: 1

      You can't transfer a theorem from between two different axiomatic systems without corrospondence, and whether or not they give different answers is meaningless - as they make different assumptions to start with.

    72. Re:Uh ... by uncmathguy · · Score: 1

      What do you mean by "more integers than primes"? Since both are infinite, the standard way of comparing sizes is to ask whether there is a 1-1 correspondence between the two sets. And there is. So in the cardinality sense, there are exactly as many primes as there are integers. And by the way, cardinality is extremely precise.

    73. Re:Uh ... by codewarren · · Score: 1

      Close, but to be 100% and O(log n) correct, Goedel proved that statement P, such that neither P nor (not P) and the set of the intersection of (not P nor not P) and (P or Q) where Q is the set of (not P and not R) and R is (not Q unless P), then such statements can only be shown to have a thruthiness of P - Q, or zero.

    74. Re:Uh ... by itsme1234 · · Score: 1

      Yes, in such a system anything will be true (as in "it is implied by the axioms" as in "it can be proved if we assume the axioms"). False implies anything. I don't think there is any "radically different logic base" that makes this any more useful, it's just some "corner case". It is worth mentioning that you might have an axiomatic system that it's not clearly contradictory (but still is) and everybody could just prove theorems "the old way" when it would be enough to show the contradiction and therefore prove any and all theorems of that axiomatic system (making it quite useless unless you remove/change some of the axioms).

    75. Re:Uh ... by TechnicalPenguin · · Score: 1

      The short version is that any sufficiently advanced system will have some way of expressing the idea "This statement is false," which the system cannot prove to be either true or false because both answers are wrong. So, as zacronos said, any such endeavor will either be incomplete (it can't express every true/false statement) or it will be self-contradictory (it can express this true/false statement, but it can't determine whether it is true or false without being wrong).

    76. Re:Uh ... by Anonymous Coward · · Score: 0
    77. Re:Uh ... by mochan_s · · Score: 1

      It was in some discussion or documentary that sort of made whim remark that Godel's incompleteness led indirectly to the creation of the computer programming languages.

      As far as I know, most modern mathematics consider a set small enough so that it is not a problem. So, for Ruseel's paradox, if you make sure you don't consider the sets of all sets, then all the good mathematics still works and the paradox is avoided. For Godel's incompleteness, there is a countable set of proofs that are free from this and that's where all known interesting proofs lie.

      But, I could be wrong. All this is from seminars and such, and I'm not a logician.

    78. Re:Uh ... by khallow · · Score: 1

      What do you mean by "grammar"? And recall Godel's Theorem holds only for sufficiently complicated systems. Simpler (and very boring) ones don't have unprovable statements.

    79. Re:Uh ... by beckerist · · Score: 1

      Right but because it can be both, it can't just be one or the other hence the contradiction OR incompleteness.

    80. Re:Uh ... by snarkh · · Score: 1

      If you cannot add (not G) as an axiom without causing a contradiction, that shows that G must be true.

    81. Re:Uh ... by hopeless+case · · Score: 1

      >What does this even mean? How can a mathematical truth be 'known" if it cannot be proven?

      I belive I can shed some light on that question.

      In any formal system, you can write out a mechanically checkable proof of a statement using the production rules of the system (a derivation of the statement if you will), or you can exhibit a model in which the statement is false (a model can also be mechanically checked for correctness).

      This roughly corresponds to an informal proof of a statement, or a counterexample in which you can show the statement to be false.

      If you can prove a statement using the production rules, then you know the statement will be true in all possible models of the system.

      So there are two formal notions of truth at play here. In the first one, you wonder whether a statement can be derived. In the other, you wonder whether it is true in all models of the formal system.

      What godel showed was the in a sufficiently power formal system, there will be statements that can't be derived, but which are still true in all models.

      How can you know that a statement X is true in all models, if you can't derive X in the formal system?

      You can use the formal system to talk about itself (which is like using a program to generate the text of another program to solve a problem, instead of writing a program to solve the problem directly), and derive the statement that "X is true in all models of the formal system". This is known as a second order proof.

      Goedel's theorem can not stop you from discovering a formal proof for any mathematical principle that a person can informally recognize the truth of. Whether that proof is first order, second order, third order, ..., however, is up for grabs.

      The other posts in which people go on about how goedel proved that people have souls because they can do something a machine can't (recognize the truth of a statement that can't be formally proved) are mistaken.

    82. Re:Uh ... by johanatan · · Score: 1

      How can there be a 1:1 correspondence? Just take a look at this sieve in action.

      As you can see, right off the bat, all of the even numbers are thrown out. So, even if you go no farther than that, there are more integers than primes.

      [And, when you include negative numbers, none of which can be prime by a standard definition of prime, then the count of integers is even more!]

    83. Re:Uh ... by masterzora · · Score: 1

      It is rather counterintuitive, actually. The mathematicians of the time were rather upset by Cantor's results and it took some time before this notion was widely accepted. I don't know what you mean by "precise", but if you mean what I think you do (and that I'm having difficulty explaining without misusing other mathematical terms, and thus won't), I'd say cardinality is precisely defined.

      A quick lesson:

      We start with the natural numbers, N = {0, 1, 2, 3, 4, 5, ...} and we see it has cardinality aleph null. Now, hopefully you can see, even if you can't see why, that the set {1, 2, 3, 4, 5, 6, .....} has the same cardinality as N despite missing the 0. In fact, one of the defining features of an infinite set is the ability to have a proper subset (that is, a subset that isn't the entire set) with the same cardinality as the entire set.

      Now, the first surprising result: the integers, Z={..., -3, -2, -1, 0, 1, 2, 3, ...}, have the same cardinality as N. We can show this using one of the basic principles of combinatorics: if you can create a bijection between the members of two sets, their cardinalities are equal.

      (This paragraph is defining a bijection. If you are familiar with that, feel free to skip this). A bijection, if you don't know, is a map from one set to another such that the map is both injective and surjective. A map simply associates a member of the first set to a member of the set you are mapping it to through some method or another (for example, f(x) = x+1 is a map from the reals to the reals (f:R->R) such that the member x is associated with the member x+1). A map is injective if distinct members from the first set map to distinct members of the second set or, equivalently, that if two members map to the same thing, those members must be equal. A map is surjective if everything in the second set gets mapped to.

      Now, to show that |Z| = |N| (Z has the same cardinality as N) we must find a bijection between them. The easiest way to do this is to find a systematic way that would list all of the members of Z given an infinite amount of time. Clearly {..., -3, -2, -1, 0, 1, 2, 3, ...} won't work since it is unbounded on both sides. However, it should be easy to see that {0, 1, -1, 2, -2, 3, -3, ...} should be work just fine, and our bijection would be that the nth member of the set would map to the nth natural number. Thus, |Z|=|N|.

      Now, this probably doesn't shock and amaze much anymore. But one that still continues to be amazing is that the rational numbers, Q={1, 1/2, 1/3, 1/4, -1, -1/2, -6/7, 3, ...}, have the same cardinality as the integers. The proof of this one is a little difficult to show in a slashdot comment, but the idea is to make a grid with numerators running across the x-axis and denominators running across the y-axis. Thus the top row would be all the members of N (the proof is easier to show using only positive numerators/denominators, but you can hopefully see from the previous example how you can throw the negatives in). If we then start with the top left-most entry (1/1=1), we can start reading off diagonals, giving us a listing like {1, 2, 1/2, 1/3, 1, 3, ...}. You'll note that we have a duplicate in this set, but it is trivial to simply skip over duplicate entries, so we can do so without affecting the cardinality. This creates a bijection between Q and N (well, technically between Q+ and N, but again, you can see how we can add in Q- and 0 trivially).

      Now, having shown that |N|=|Z|=|Q|, one might think that maybe |R|=|N| (where R is the reals). Cantor further showed that this isn't true. In fact, |[0,1]| > |N| (that is, the cardinality of the reals between 0 and 1 is greater than the cardinality of the natural numbers). Again, this one is easier to show given something to draw on, but I'll make do. Assume you can list all of the reals between 0 and 1. Just make an infinite list of as ma

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    84. Re:Uh ... by johanatan · · Score: 1

      Yes, but correspondence is rather common. A few examples come to mind:

      algebra & geometry (and various forms of each),
      number theory, graph theory & set theory

      Different 'answers' are only meaningless if the two systems do not correspond. If I'm not mistaken, that would be the exception rather than the rule.

    85. Re:Uh ... by uncmathguy · · Score: 1

      Yes, not every correspondence between integers and primes will be 1-1, but that doesn't mean there isn't one which is. First, consider the following 1-1 correspondence between the positive integers and the primes: 1 -> 2, 2 -> 3, 3 -> 5, 4 -> 7, 5 -> 11, etc. That is, to the nth positive integer, we associate the nth prime.

      Now to get a 1-1 correspondence between the primes and the integers, we simply need a 1-1 correspondence between the integers and the positive integers: 0 -> 1, 1 -> 2, -1 -> 3, 2 -> 4, -2 -> 5, etc. Then clearly going from integer to positive integer to prime gives a 1-1 correspondence. Isn't math fun?!

    86. Re:Uh ... by johanatan · · Score: 1

      So, cardinality is precise--that wasn't the right word. But, it is somewhat artificial and abstract. To put this in geometric terms, the entire 'proof' hinges on taking a line and turning it into a ray (which you could picture as picking a point on the line and pulling it out perpendicularly until the two rays formed by the picking of the point lie on top of one another). And, that's obviously losing some information (all of the information of one of the original rays, i.e., the negative numbers in your example).

      Cardinality is simply an artificial construct and does not entirely capture the real nature of things. It may be that we came to this result by including an improper axiom. I.e., maybe reality is beyond this mode of looking at the world. Maybe (and I entirely suspect this is the case) reality is beyond all modes of looking at the world.

      This is the interesting thing about Godel, to me. Models work in isolation; but when they reach a certain critical mass, they start to break down.

      In this particular case, maybe we need another definition of cardinality that doesn't lose the intuitive nature of the relationships between the sizes of these sets). Also, of course, the fact that zero is a special number (though even it is a somewhat abstract creation) plays a big role in this, but I think that your 'trick' would work even if you had picked another number besides zero to be the bounded endpoint).

    87. Re:Uh ... by johanatan · · Score: 1

      Well, that is an interesting trick (and I've just responded to this in another post as well--maybe we you could join the discussion there)?

      Math is fun, but at some point, it starts to lose information which we intuitively know to be true (and thus it's applicability to the real world is limited).

    88. Re:Uh ... by masterzora · · Score: 1

      I have to admit, you've lost me with this post. To begin with, I can't make much sense of your geometric description or how my (admittedly rushed and slightly handwaved, though there exist far more formal and robust forms of them) proofs hinged on it. The proofs I used hinged on one of the basic principles underlying a very rich and important field, combinatorics. This principle is that the ability to create a bijection between two sets implies equal cardinality and the provable inability to do so implies unequal cardinality. Further, the simple fact that there exists these bijections means that no information is being lost. As long as you have one set and a bijection between it and another set, you have that second set and all the information it contains.

      Cardinality is not an artificial construct. It's a measure of how many things there are. It's easy to see |{1,2,3}| = |{cat, bird, dog}| = 3 and that there's nothing artificial about this. Your issue is with the extension into the infinite, which is perfectly understandable since infinity is a pretty abstract and difficult concept. Thing is, it's a very real and very useful concept, so we're not ditching it any time soon.

      Consider the history of mathematics: natural numbers are a given. I mean, as soon as you have a concept of "how many" in any way (which is a pretty basic concept", the natural numbers quickly follow. Even fractions are relatively intuitive, as you can have a pie and cut it into two pieces. It is obvious that neither piece is a pie, but that both together are, so we have 1/2. Then we get the concept of 0. How can nothing be a number? Then we introduce the concept of negative numbers. Negative numbers were considered absurd and meaningless until very recently. Hell, Euler believed negative numbers to be greater than infinity and therefore safely ignored. Irrationals were accepted a long time ago, but they caused a lot of unrest when it was first proved that there exist some numbers that are not rational. As it turns out, they are labeled "irrational" because they were thought to make no sense. In a similar vein, the imaginary numbers were named as such by Descartes because they clearly could not be possible, yet they are important in many applications today. Fortunately, people were far more willing to accept the quaternions (a four-dimensional non-commutative extension of the complex numbers) and the octonions (an eight-dimensional non-associative extension of the quaternions), but I'm willing to be that the concepts of these two still boggle your mind (took me a while to get used to them, anyway).

      Infinity, and the different cardinalities therein, are kind of the same way as all of these numerical extensions with the being non-intuitive, but still correct and useful. There is no need to really get a new definition of cardinality given that the one we have works for everything we know and provides useful results. Much like with the irrationals, the negatives, the complex, etc, it's a useful concept that one needs to learn to adjust to and it will make a lot more sense. Intuition, as it turns out, does need some training to be useful.

      Also, I don't get your last sentence or in what way I depended on zero....

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    89. Re:Uh ... by uncmathguy · · Score: 1

      Maybe what you are looking for, instead of cardinality, is the "is a proper subset of" relation. For it is certainly true that the primes are a proper subset of the integers -- there are integers which are not primes, but every prime is an integer. And while it is certainly useful to have the proper subset relation in math (and thus, why we have it), it is very different than cardinality.

      Cardinality is a measure of the size of the set, not necessarily the relationship to other sets. In fact, consider the sets A = {1, 2, 3, ...} and B = {-1, -2, -3, ...}. Neither is a subset of the other. Yet we can still compare them by saying that they have the same size (cardinality).

      Perhaps why all this cardinality business seems a little counter-intuitive is because often in common language when we say one collection is larger than the other, we aren't entirely clear about in which sense we mean: size or proper subset. Indeed, for any finite sets A and B, if A is a proper subset of B, then A has smaller cardinality than B. This does not necessarily hold if A and B are infinite.

    90. Re:Uh ... by johanatan · · Score: 1

      I have to admit, you've lost me with this post. To begin with, I can't make much sense of your geometric description or how my (admittedly rushed and slightly handwaved, though there exist far more formal and robust forms of them) proofs hinged on it. The proofs I used hinged on one of the basic principles underlying a very rich and important field, combinatorics. This principle is that the ability to create a bijection between two sets implies equal cardinality and the provable inability to do so implies unequal cardinality. Further, the simple fact that there exists these bijections means that no information is being lost. As long as you have one set and a bijection between it and another set, you have that second set and all the information it contains.

      This proof works in such a way as to confer equality on two sets whilst the two sets in question are intuitively (i.e., at finite scales) different in size. I thought the point of aleph numbers was to distinguish between various degrees of infinity. In this case, if both N and the prime numbers have the same aleph number, then the aleph number is not precise enough and we need something which captures the *speed* at which these cardinalities grow to infinity. If aleph numbers don't capture that (or don't capture it at this granularity), then it would be nice to have some augmented aleph numbering system which would capture it).

      You agree that aleph one represents a greater infinity than aleph null, no? Do you also agree that with the bijection you defined between N and the primes, the primes grow faster towards infinity than do the members of N? Therefore, in my mind, the infinity that the primes are growing to is larger than the infinity that the naturals grow to (or alternatively the infinite cardinality of primes is smaller than the infinite cardinality of naturals, i.e., not every natural is a prime).

      Also, I don't get your last sentence or in what way I depended on zero....

      Zero was of interest because it was the first number of the set: {0, 1, -1, 2, -2, 3, -3} which was used to prove that |Z| == |N| (which is really only interesting as background information on our way to the proof of the equality between the cardinalities of N and the primes). Like I said previously though, I don't think you had to choose zero there. You could've had a set that looked like this for instance:
      {18, 19, 17, 20, 16, 21, 15, ...} and that would've been analogous to pick 18 to 'pull' from the line as in my geometric description. After having written that, I'm now pretty convinced that the specialness of zero had nothing to do with this proof.

    91. Re:Uh ... by Anonymous Coward · · Score: 0

      Yes, precisely. I misunderstood the aleph numbering system to refer to the proper subset sense. Do you happen to know if there is a numbering system which takes into account the proper subset relation?

    92. Re:Uh ... by Anonymous Coward · · Score: 0
      Actually, this comment from wiki on the 'cardinal number' page explains it all:

      It is also possible for a proper subset of an infinite set to have the same cardinality as the original set, something that cannot happen with proper subsets of finite sets.

      The cardinality number thus can lose the information about the actual proportions of the sets in question (in the case of infinite sets).

      P.S. This is 'johanatan' as I've exceeded my daily limit already.

    93. Re:Uh ... by masterzora · · Score: 1

      Sets have no notion of "growing to infinity" or the "speed" at which they do so. They are simply collections of things. And there are as many things in the set of all primes as there are in the set of all natural numbers. The reals have a higher cardinality than the set of naturals, not because they "grow to infinity" faster or anything silly like that, but because there are simply more of them there.

      And, yes, I agree aleph_1 > aleph_0. I don't agree that in my bijection that the primes grow faster, though I will agree that the nth prime will be larger than the n-1th by more than n in general. But the important thing is that they're not really "growing to an infinity" because infinity isn't a number (even if we do say infinite number, it's more a convenience of ambiguous terminology than anything).

      And, even more importantly, the cardinality of a set isn't what it "grows to" as you keep saying, as that doesn't even make sense.

      If you allow me a small aside on how that doesn't make sense, it will become clear. Firstly, for your notion to make sense, we would have to say that |{2,3,4,5}| = 5 since it clearly "grows to" 5 in your words, but we should be able to see that |{2,3,4,5}| = 4. Cardinality is a measure of how many things are in a set not how large are the things in the set.

      Another, hopefully illuminating, related bit: take the sets of the first n natural numbers and the first n prime numbers. Say, n=5, so we have N_5 = {1,2,3,4,5} and p_5 = {2,3,5,7,11}. Surely we can both agree that the cardinality of both of these is 5 and the fact that the set of primes "grows faster" doesn't change that. All that we care about is *how many things are in it*.

      You are correct in that the choice of 0 to begin with isn't necessary, but it is convenient because we do need some manner of ordering them algorithmically. Another possible ordering that fulfills order is {6, 2, 5, 0, 1, -2, -1, 3, -3, 4, -4, -5, -6, 7, -7, 8, -8, 9, -9, ...}.

      --
      Remember, open source is free as in speech, not free as in bear.
    94. Re:Uh ... by masterzora · · Score: 1

      You'll note that this property that you quote is one I listed as an important distinguishing feature of infinite set that makes these seemingly impossible truths possible.

      Just because a proper subset has the same cardinality doesn't mean information is lost. Again, the fact the map from the one set to the other is a bijection means there's a map from the other set to the one, restoring the first set. Given either set and the bijection, you *have* the other set regardless, so no information is lost.

      --
      Remember, open source is free as in speech, not free as in bear.
    95. Re:Uh ... by slawekk · · Score: 1

      Mizar library would be an attractive target to import. It is the best library of formalized mathematics in existence. The problem is that then you would have to make Mizar the back end of the wiki, but Mizar is not free software. Writing an alternative parser for the Mizar language would be very difficult, people have tried to do that and failed. Also, there are copyright issues with trying to import the Mizar library.

    96. Re:Uh ... by johanatan · · Score: 1

      And there are as many things in the set of all primes as there are in the set of all natural numbers. The reals have a higher cardinality than the set of naturals, not because they "grow to infinity" faster or anything silly like that, but because there are simply more of them there.

      I think it's rather silly to split hairs, but that's just me. Anyway, since you seem to be in the business of splitting hairs, I will indulge you.

      Let me give you a quick proof that there are not as many things in the set of primes as there are in the set of natural numbers:

      1. A proper subset contains fewer things than its superset.
      2. The set of all primes is a proper subset of all naturals.
      ... (Therefore) The set of all primes contains fewer items than the set of all naturals (i.e., the cardinality of the set of all primes is smaller than the cardinality of the set of all naturals).

      I suspect the only reason we have this disagreement is because you start from a different set of axioms and/or take a different route to arrive at the knowledge you so want to prove me wrong with. [And, btw, you're the one who brought the word cardinality into this. I was speaking of degrees of infinities which may be thought of as aleph numbers and thus cardinalities --or-- as a more proper degree which respects some other (and more important to some) things that we know about sets].

      But, once again, this sort of collision of models is entirely expected given Godel's theorem. The 'problem' here can be looked at in several ways but since you did not understand my geometry illustration and since you do not seem to want to learn anything from me (or to even think that is possible for you to do so, I will not be wasting my time going in to these additional insights).

      And, yes, I agree aleph_1 > aleph_0. I don't agree that in my bijection that the primes grow faster, though I will agree that the nth prime will be larger than the n-1th by more than n in general.

      Well, if you realize that, then you should be well on your way to understanding the proof I gave above.

      But the important thing is that they're not really "growing to an infinity" because infinity isn't a number (even if we do say infinite number, it's more a convenience of ambiguous terminology than anything).

      And, even more importantly, the cardinality of a set isn't what it "grows to" as you keep saying, as that doesn't even make sense.

      If you allow me a small aside on how that doesn't make sense, it will become clear.

      You've got to be kidding me. Of course it is a convenience, that's why I used it. However, it becomes much less convenient when people start splitting hairs like this.

      Firstly, for your notion to make sense, we would have to say that |{2,3,4,5}| = 5 since it clearly "grows to" 5 in your words, but we should be able to see that |{2,3,4,5}| = 4.

      I was speaking of the density of the set. When you do your neat folding trick where you take all the negatives and you put them in with the positives with zero at the beginning, are you not doubling the number of numbers that come after zero in that set? The geometric analogy I provided would've shown you this if you'd understood it. [And, if you don't believe this statement, I can prove it.]

      Cardinality is a measure of how many things are in a set not how large are the things in the set.Another, hopefully illuminating, related bit: take the sets of the first n natural numbers and the first n prime numbers. Say, n=5, so we have N_5 = {1,2,3,4,5} and p_5 = {2,3,5,7,11}. Surely we can both agree that the cardinality of both of these is 5 and the fact that the set of primes "grows faster" doesn't change that. All that we care about is *how many things are in it*.

      Ok, now do this. Take the first n positive numbers where n=5: {1, 2, 3, 4, 5}. Now, of tho

    97. Re:Uh ... by johanatan · · Score: 1

      Yes, precisely. I misunderstood the aleph number system to consider the proper subset sense. Do you happen to know if there is an infinity degree numbering system which takes into account the proper subset relation?

    98. Re:Uh ... by Darby · · Score: 1

      How can a mathematical truth be 'known" if it cannot be proven?

      Well, *assume* for the moment that...say... the Goldbach conjecture is shown to be undecidable. This means that it can not be proven or disproven (from within the system). Therefore, it has to be true.
      Why you ask? Well, if it were to be false, then you would be able to come up with integers which violate it. But then you would have proven it false and hence contradicted the undecidability.

      So it cannot be proven yet nonetheless, it's now a known truth.

    99. Re:Uh ... by Darby · · Score: 1

      The continuum hypothesis says there is a set bigger than the integers but smaller than the reals.

      Well, close....in the sense that most of the words are accurate. The hypothesis was that there is *not* such a set.

      Also, you can't necessarily say that you'll get consistent mathematics by adding an undecidable statement to existing axioms. You also have to know that the existing axioms are already consistent. ZF set theory has not been shown to be consistent, and in fact, it has been proven that it can't be proven to be consistent from within the theory itself...well, that is...unless it actually is inconsistent.

      Yeesh, I think I liked functional analysis better than formal set theory and that's saying something.

    100. Re:Uh ... by Darby · · Score: 1


      Cardinality is simply an artificial construct and does not entirely capture the real nature of things.

      No, No, No.

      It does capture the real nature of things. Their real nature might be unintuitive, but it absolutely, brilliantly does capture the real nature of *infinite* things.

      Say I have 5 pebbles in one hand and 5 coins in the other. Would you agree that the "5ness" contained in each of my hands is a real thing. You can take one pebble and one coin, then another and then another until my hands are empty. Each coin will be matched up with one *and only one* pebble.

      The problem is not at all that it doesn't capture the real nature of things, it's that your intuition is not geared to deal with infinite quantities. That's what makes mathematics so freaking powerful. It can conclusively demonstrate things which you, quite reasonably mind you, would automatically assume to be obviously false.

      Making a statement that the cardinality of the primes is exactly equal to the cardinality of the rationals doesn't lose any information about either. Primes are still indivisible, and rationals are still all the ratios of all the integers (barring zero denominators, of course) every other true statement about either is still true. You only gain *more* information about them,which can be incredibly useful.

      This is the interesting thing about Godel, to me. Models work in isolation; but when they reach a certain critical mass, they start to break down.

      Again, no. The only thing that is broken down by this is your intuition. The "models" work better than ever with this than they ever could without it. You have no idea how much mathematics would not exist without this.


      In this particular case, maybe we need another definition of cardinality that doesn't lose the intuitive nature of the relationships between the sizes of these sets).

      No, that's exactly what you don't need. Reality need not conform to your preconceptions.

      You are stuck in a rut based on your long experience with finite quantities. Cardinal numbers (well, the infinite ones anyhow) are not part of the system of numbers which you are familiar with. They are characteristics of sets. Just like coins and pebbles are entirely different things, but when I hold 5 in each hand those collections share a certain property. The property of "5ness".

      Infinities work differently. This is a proven fact (not a well verified theory, but an absolute and unassailable fact.) which is extremely important and incredibly useful. Cardinality does maintain the intuitive relationship you like as long as you are talking about finite sets. Once you hit the first infinity, things change. But the concept of cardinality and the definition of equal cardinality doesn't change at all by crossing that boundary. The fact that we don't need to change it to meet our finite intuition gives us new information.

      Is it just that you don't like the particular example the OP gave? Are you comfortable with the fact that infinity+1=infinity, 2* infinity = infinity ( taking "infinity" to mean the smallest infinity here)? If so, then you already know and accept that the naturals have the same number of numbers as the naturals plus zero. You already know and accept that there are *exactly* as many positive integers as there are integers. Infinity * infinity = infinity expresses the fact that the naturals and the rationals have the same exact "number" of numbers.

      This might be unintuitive, but it's not at all arbitrary and you can't define cardinality in such a way as to make this go away without making it a completely meaningless or inconsistent idea. It is an inherent property of the way things are....OK, "things" being the sets of numbers in question anyhow.

    101. Re:Uh ... by Darby · · Score: 1

      I think it's rather silly to split hairs, but that's just me. Anyway, since you seem to be in the business of splitting hairs, I will indulge you.

      It's not "splitting hairs", it's called being precise which is critical.


      Let me give you a quick proof that there are not as many things in the set of primes as there are in the set of natural numbers:

      1. A proper subset contains fewer things than its superset.

      OK, your first assumption is demonstrably false, therefore your entire argument is unsound. The OP (and a few other people as well) have absolutely positively and beyond the possibility of a doubt demonstrated that to be the case. The problem is that you are using ambiguous terms in an attempt to prove something. You must have well defined terms or you are not going to be capable of constructing a logical argument.
      What does it mean for a set to "contain fewer things" than another set? For finite sets, you can lay them out side by side and you are done. For infinite sets you'll never even get close to finishing so you need a more precise way of stating that relationship.


      I suspect the only reason we have this disagreement is because you start from a different set of axioms and/or take a different route to arrive at the knowledge you so want to prove me wrong with. [And, btw, you're the one who brought the word cardinality into this. I was speaking of degrees of infinities which may be thought of as aleph numbers and thus cardinalities --or-- as a more proper degree which respects some other (and more important to some) things that we know about sets].

      The only disagreement is between your intuition and the way things actually are. "more proper" "things we know about sets" These statements do not make any sense. You are talking about how finite sets work and demanding that infinite sets must conform exactly to finite sets.


      But, once again, this sort of collision of models is entirely expected given Godel's theorem. The 'problem' here can be looked at in several ways but since you did not understand my geometry illustration and since you do not seem to want to learn anything from me (or to even think that is possible for you to do so, I will not be wasting my time going in to these additional insights).

      No, it has nothing at all to do with Godel's theorems. There is no "collision of models". You are not conveying "insights", you are only conveying your lack of understanding of the subject.

      Well, if you realize that, then you should be well on your way to understanding the proof I gave above.

      That wasn't a proof. It was an unsound argument based on known false assumptions.

      You've got to be kidding me. Of course it is a convenience, that's why I used it. However, it becomes much less convenient when people start splitting hairs like this.

      He wasn't splitting hairs. He's absolutely right, and you are absolutely wrong.

      I was speaking of the density of the set. When you do your neat folding trick where you take all the negatives and you put them in with the positives with zero at the beginning, are you not doubling the number of numbers that come after zero in that set? The geometric analogy I provided would've shown you this if you'd understood it. [And, if you don't believe this statement, I can prove it.]

      Do you even know what density is? Don't worry, you don't. It is a well defined term and it does not apply to sets. Sets have no order, they have no concept of distance between numbers or anything of the sort. No, you can not prove it. The OP already proved it to be false. You just do not understand the ideas under discussion. It's ok, they're not simple concepts, but they are very well understood.

      Ok, now do this. Take the first n positive numbers where n=5: {1, 2, 3, 4, 5}. Now, of those, which are primes? 2, 3, 5. Hmmm, only 3. There are more naturals than primes.

      Here is a nice analogy of what you just did:

      Take the set {3,5}. Wow, they're

    102. Re:Uh ... by johanatan · · Score: 1

      Ok, how about this thought experiment.

      [This will at the same time address masterzora's gripes with my use of the word infinity and the concept of growing to infinity (both of which mind you I got from years of sitting in mathematics classes).

      Take two children and give them an endless supply of marbles and each a container. Also give one child the ability (or a machine) to tell if a given number is prime). Then start the first child at the number one and tell him to count til he can count no more putting one marble in his container for each number he 'counts'.

      Tell the second child to put a marble in his container anytime the first one calls out a prime.
      I think you and I could both agree that the first child will have many more marbles than the second in his container before too long and that as more time passes, the larger the first's count of marbles will be in proportion to the second (i.e., the first child's marble count will grow at a constant rate whilst the second child's marble count will grow at an ever decreasing rate).

      [This thought experiment should be able to be expanded to a formal inductive proof if that is what you want.]

      Let me also state, that I completely understand the OP's proof. I just think that it isn't the whole story. [And, BTW, the first assumption from my proof is only false when talking about infinite sets. I cannot say that I know all of the math behind why infinite sets are allowed to break the intuitive definition of cardinality, but if it is like alot of things in math, it could be an arbitrary decision. And, if that is the case, then by simply changing that decision and the axioms involved, we could enter other and seemingly to me useful areas of math.

      Math is dependent on the axioms (or at least the logic portion of it). I can choose the axioms I want whether or not they fit with your view of reality. Granted, it may not mean much, but in this case, I think that an alternative axiom set could produce interesting results.

    103. Re:Uh ... by adavies42 · · Score: 1

      For example the continuum hypothesis was shown to be independent of the axioms of the set theory.

      This is actually something I've wondered about for a while. AFAICT, the Continuum Hypothesis isn't so much undecidable as under-specified (and thus has nothing to do with Godel). It's like Euclid's 5th postulate--you can either take it or its negation(s, in the case of Euclid), and derive a different system either way. Or does it make sense to say that Euclid's 5th is undecidable in the context of the other four?

      IANAMathematician, so if I'm completely off base here, please tell me.

      --
      Media that can be recorded and distributed can be recorded and distributed.
      -kfg
    104. Re:Uh ... by MadMidnightBomber · · Score: 1

      Yes, but it no-one claimed that the system would be complete, just that it would be consistent - which is perfectly possible and not really any different to the way we all do maths right now.

      --
      "It doesn't cost enough, and it makes too much sense."
    105. Re:Uh ... by MadMidnightBomber · · Score: 1
      Gaaah! Goedel proved that no sufficiently complex system (at least integer arithmetic) could be consistent and complete. Meaning, that there would be at least one true statement which was not provable or that there would be one false statement which was provable.

      It is perfectly possible to collect a set of proofs, all of which are correct and provable in a given system.

      --
      "It doesn't cost enough, and it makes too much sense."
    106. Re:Uh ... by snarkh · · Score: 1

      You are a little bit off base, but not too much :)
      Undecidable and "underspecified" is the same thing. Godel showed that _any_ system of axioms is either contradictory or underspecified (meaning that something like the fifth postulate exists). Cohen showed that the Coninuum Hypothesis is independent of the standard axioms for set theory (Zermelo-Frenkel axioms). So you are right, it is exactly like the fifth postulate, on the other hand it is an example of incompleteness.

    107. Re:Uh ... by Free+the+Cowards · · Score: 1

      Well no, if it's shown to be undecidable then either it's true or there exists some counterexample. Just because nobody has found it yet doesn't mean it's not there. And since it's impossible to search all of the integers looking for one, you can never say that one doesn't exist, unless you actually prove the thing to be true. Thus it would not be "known", because it could be either true or false.

      --
      If you mod me Overrated, you are admitting that you have no penis.
    108. Re:Uh ... by Darby · · Score: 1

      Ok, how about this thought experiment.

      It fails utterly. Any "thought experiment" you can possibly come up with will likewise fail just as utterly. That's the difference between intuition and proof. Your intuition is wrong. Dead wrong. Absolutely, positively wrong.

      Here's one reason why:

      [This thought experiment should be able to be expanded to a formal inductive proof if that is what you want.]

      No, it can't. Not to prove what you're trying to prove. Induction can only prove a statement true for all *finite* values of 'n'. So, yes, obviously once you pick a specific fixed number, n, if you take the set of all natural numbers up to and including n and compare that with the set of all primes up to and including n (assuming n is prime of course, otherwise it's not included) then your first set will be larger.

      That's all well and good for what it is, but it has no bearing whatsoever on what you're attempting to demonstrate.


      Let me also state, that I completely understand the OP's proof. I just think that it isn't the whole story.

      Then you do *not* understand the OP's proof *at all*. You don't even understand what a proof is.

      And, BTW, the first assumption from my proof is only false when talking about infinite sets.

      But that's all we're talking about. Both the primes and the naturals are infinite sets, so in the context of the discussion your assumption is absolutely false. In fact the truth or falsehood of your assumption depends entirely upon whether the set in question is finite or infinite. The negation of your statement can, in fact, be taken as the *definition* of an infinite set. It's absolutely true that a set meeting the negation of your statement is always infinite. It's also true that any set meeting that criteria must be infinite.

      I cannot say that I know all of the math behind why infinite sets are allowed to break the intuitive definition of cardinality, but if it is like alot of things in math, it could be an arbitrary decision.

      They are not "allowed" to do anything. They do. They did so long before Cantor developed the theory of the infinite and proved it absolutely. It's an inherent property of infinity.

      There isn't an intuitive "definition' of cardinality. There is intuition. There is a definition of sets having the same cardinality. These are 2 different things. Very rarely if ever are decisions about definitions or axioms "arbitrary". It might well be the case that it's possible to choose one of 2 mutually contradictory options in some given situation without "breaking" anything, but which one to go with is generally chosen based on which one creates more interesting mathematics. Physicists have different ideas about such things. This is why, IIRC, mathematicians generally like the Axiom of Choice as it leads to many interesting consequences while physicists generally don't like it because it leads to pathological cases like unmeasurable sets. The decisions aren't arbitrary in general.

      Math is dependent on the axioms (or at least the logic portion of it). I can choose the axioms I want whether or not they fit with your view of reality. Granted, it may not mean much, but in this case, I think that an alternative axiom set could produce interesting results.

      You're certainly welcome to make up whatever you like, but you'd be best served by actually doing so rather than claiming that somehow your unstated (and most likely not very well thought out) new axioms should be treated as if they have any value. This is especially true given that you haven't proposed any problem with the existing mathematics, or anything interesting you hope to gain from the exercise. The fact that you don't find something intuitively obvious is completely meaningless as to the value of the mathematics, it only demonstrates a lack of imagination and a lack of effort to understand on your part.

    109. Re:Uh ... by Darby · · Score: 1

      Well no, if it's shown to be undecidable then either it's true or there exists some counterexample.

      You don't know what "undecidable" means is all that you've said. If it's undecidable, then it can not be shown to be true or false. from within the system. Providing a counterexample would prove it false within the system. If it's true or there exists a counter example, then it is decidable.

      And since it's impossible to search all of the integers looking for one, you can never say that one doesn't exist,

      That is totally irrelevant. All you said there is that providing examples for a statement does not constitute a proof which is certainly true but has nothing to do with the point. Undecidability *proves* that there can not possibly exist a counter example. It's just not done from within arithmetic.

    110. Re:Uh ... by Free+the+Cowards · · Score: 1

      Your system of statements either shows the Goldbach Conjecture to be true/false or it doesn't. If it does, then that is proof to go with your knowledge. If it doesn't, then it is not "known".

      Your whole idea seems to hinge on "within arithmetic". Well I don't care what system you work in. Either you have a proof of truth/falseness or the fact is not known. Maybe that proof involves a proof of undecidability within a certain system, but it doesn't matter.

      --
      If you mod me Overrated, you are admitting that you have no penis.
    111. Re:Uh ... by Darby · · Score: 1

      Your whole idea seems to hinge on "within arithmetic". Well I don't care what system you work in. Either you have a proof of truth/falseness or the fact is not known. Maybe that proof involves a proof of undecidability within a certain system, but it doesn't matter.

      Thank you for the compliment, but it's not my idea. The person you're looking for is Kurt Gödel. If you're going to attempt to rationally discuss his results you might consider taking a few minutes to actually understand the statement of them.
      "within arithmetic" is absolutely essential...or within whatever system you're dealing with. The Goldbach conjecture is stated within arithmetic, so it's the only system that matters for this. The fact that it's possible to prove things about arithmetic from the outside is perfectly in line with his theorems.
      There is no problem with this.

    112. Re:Uh ... by Free+the+Cowards · · Score: 1

      Let's back up a moment. All I've been saying about Godel's theorem is that it doesn't have anything to do with the question of whether this wiki's goal makes sense. I assert merely that if a piece of mathematical knowledge is truly known, then it has a proof, and that if it has a real proof then that proof can be checked by a machine.

      Since humans are machines, this would seem to be true in a very obvious way.

      If I am wrong, please elucidate.

      --
      If you mod me Overrated, you are admitting that you have no penis.
    113. Re:Uh ... by El+Cabri · · Score: 1

      Basically yes, but we're not interested in contradictory systems anyway, so that leaves us with systems that are incomplete.

    114. Re:Uh ... by Darby · · Score: 1

      Let's back up a moment.

      Fair enough.

      All I've been saying about Godel's theorem is that it doesn't have anything to do with the question of whether this wiki's goal makes sense.

      True. Several people have been arguing that it did, but they're all wrong because they've either completely misunderstood Gödel's theorems or misunderstood the goal of this project.

      I assert merely that if a piece of mathematical knowledge is truly known, then it has a proof, and that if it has a real proof then that proof can be checked by a machine.

      Yes, absolutely. Sorry for the misunderstanding.
      I must have implicitly added more to what you were saying about that bit than you actually were.

      Since humans are machines, this would seem to be true in a very obvious way.

      Makes sense, although just because we can do something doesn't necessarily mean that the engineering problem of building a machine to do the same thing is surmountable. Eventually, I'd like to think that it will be, but who knows. Given the limits of this project, it would seem reasonable that it's doable, although I don't really know enough about formal verification and the like to say.

    115. Re:Uh ... by johanatan · · Score: 1

      Here's one reason why: [This thought experiment should be able to be expanded to a formal inductive proof if that is what you want.] No, it can't. Not to prove what you're trying to prove. Induction can only prove a statement true for all *finite* values of 'n'. So, yes, obviously once you pick a specific fixed number, n, if you take the set of all natural numbers up to and including n and compare that with the set of all primes up to and including n (assuming n is prime of course, otherwise it's not included) then your first set will be larger. That's all well and good for what it is, but it has no bearing whatsoever on what you're attempting to demonstrate.

      You obviously don't know as much as you claim to know. Read and be enlightened:

      http://en.wikipedia.org/wiki/Mathematical_induction

      That's definitely about 'infinite' sets.

      There isn't an intuitive "definition' of cardinality. There is intuition. There is a definition of sets having the same cardinality. These are 2 different things.

      There is a 'definition' of sets having the same cardinality. Yes, and it is this 'definition' which is flawed and arbitrary. It fails to account for the rates at which things grow to infinity (which is precisely the thing I want to capture with some augmented aleph number--call it a 'bet' number if you like).

    116. Re:Uh ... by johanatan · · Score: 1

      Well, actually, the way we do maths right now is very compartmentalized. Each theory has its own set of axioms and all of its theorems apply only to those axioms. Unless this system in question keeps all these theories separate, collisions are inevitable and it will be a race to see which theorems get there first.

      I'm sure the system in question isn't going to be as sophisticated as I'd like (they never are), so it will most likely keep each theory separate and there will thus be no problems. But, of course, we will not have any greater chance than we do now at discovering these interesting 'collisions' which may provide the answer to such questions as why quantum mechanics and general relativity do not mesh (for instance).

    117. Re:Uh ... by uncmathguy · · Score: 1

      So that you don't sound too ignorant when you talk about mathematical induction, let me clarify something for you. Mathematical induction can be used to prove a property of every member of an infinite set. It can not, in general, prove a property about the infinite set itself (without going into transfinite induction, which is tricky, and definitely depends on a very precise notion of infinity).

      In your thought experiment, you "inductively" proved that for every natural number n, the number of natural numbers less than n is greater than the number of primes less than n. And this is true. However, it takes a (incorrect) leap to go from that to say that the entire set of natural numbers is larger than the entire set of primes. See the difference?

    118. Re:Uh ... by uncmathguy · · Score: 1

      I'm not entirely sure what you would be looking for. Besides the cardinal numbers, another system for dealing with infinite sets is the ordinal numbers. However, the ordinal corresponding to the set of primes is the same as the ordinal corresponding to the set of natural numbers (both are omega).

      Really, I don't see why such a system would be needed, even if it were possible. What's wrong with saying that yes, both the set of primes and the set of natural number (or integers, if you prefer) are infinite, but it turns out that the primes are a proper subset of the natural numbers. That seems to capture more information that saying the the set of natural numbers are "bigger" than the set of primes.

      The more I think about it, the more I wonder why the surprise is that one infinite set is not larger than another infinite set. For me, when I first ran into this stuff, I was much more surprised that there might be different sizes of infinity. If anything, it is that which goes against our intuition. Thoughts?

    119. Re:Uh ... by Free+the+Cowards · · Score: 1

      I'm glad we resolved our differences. As for formal verification, I don't know a great deal about it, but my understanding is that with this wiki, the human is still responsible for writing out the proof in fairly exacting detail, and the computer just makes sure that each step logically and directly follows from the previous ones. The process is made easier by allowing the use of previously-verified theorems rather than having to spell out every step down to the axioms, like calling subroutines in a program. Whether the existing programs are able to encompass all of mathematical knowledge is something I couldn't say.

      Anyway, I don't know about the technical feasibility of the project, although the founders (obviously) seem to think it's doable. My only objection is to those who think that a simple "Godel" is enough to sink it.

      --
      If you mod me Overrated, you are admitting that you have no penis.
    120. Re:Uh ... by johanatan · · Score: 1

      In that case, I suppose I should fill in the gap that was leaped over.

      The introduction of 'infinity' into this allows for time to be factored out of consideration. That's perfectly fine and I'm sure there's a lot of useful discoveries that have come out of that. But, it isn't the only route forward. You [and everyone else] seem to think that given an number, you can always get one more number by adding one to it. Or, that given a prime, you can always get another prime greater than the one you have. And, yes both of those statements are true. But, infinity is merely a concept. You can ascribe it to both of these if you wish, but I simply think that loses some information about the relation. Maybe another concept is called for? Or, maybe I'm ignorant of the existence of this other concept. I'm sure the mathematicians at the time of Cantor would've thought of this.

    121. Re:Uh ... by Darby · · Score: 1

      You obviously don't know as much as you claim to know. Read and be enlightened:

      I am quite familiar with the PMI, thanks. Hopefully uncmathguy cleared up your error to your satisfaction.

      Yes, and it is this 'definition' which is flawed and arbitrary.

      It's not at all arbitrary. It's very well thought out and exactly captures the idea of equality of size for finite sets. If it has any flaws, you have yet to demonstrate a single one.

      It fails to account for the rates at which things grow to infinity (which is precisely the thing I want to capture with some augmented aleph number--call it a 'bet' number if you like).

      It doesn't "fail to account" for it. That entire concept is completely irrelevant to the topic. Nothing is growing or changing. The only thing under discussion when talking about whether 2 sets have equal cardinality are the 2 sets themselves. Two fixed and unchanging sets. Nothing is growing, nothing is changing, and absolutely nothing is in any way shape or form growing to infinity.

      You seem to be talking about limits, but those don't even exist in this context. Limits require more structure than just sets. Heck, "growing" requires more information than exists in the concept of sets.
      {1,5,7} is *exactly* the same set as {7,1,5}. They look different to you, because the elements of the set are in a different order, but the concept of order doesn't even apply to sets. That requires a different concept called ( conveniently enough ) an "ordered set" which is a set *and* an order relation defined on that set..
      Further, you can't even say that 5 is 4 more than 1 in this situation since the concept of distance (or arithmetic or anything of the sort ) doesn't exist here. Doing that would require at least a metric space.
      Cardinality applies to plain ordinary sets with no additional structure imposed upon them, so most of the words you're using *can't* be applied in general.

      There already are beth numbers, but they don't do what you want either. Most likely that is because you don't even understand what it is that you're objecting to. You need to be able to clearly and unambiguously state what you mean. You haven't done that yet. You just keep complaining about how some things work. You need to understand what we're talking about before you're going to be able to actually understand if there even is any issue or path forward to anything interesting though.

      Your complaint about my critique of your attempt at a proof by induction demonstrates a deep flaw in your understanding of the topic under discussion.

      * From your response to uncmathguy;

      But, infinity is merely a concept. You can ascribe it to both of these if you wish, but I simply think that loses some information about the relation.

      And again, you fail to mention one single scrap of information that could possibly be "lost". It's an absolute fact that you're dead wrong on that. Maybe what you want to say is that there is a different relationship that you are interested in which is not illuminated by this, but that is a completely different thing. If you want to get anywhere in mathematics or any other area based on rational thought, you are going to have to learn how to speak precisely about whatever it is that you think you're talking about.

      Maybe another concept is called for?

      To do what? The problem is that you haven't come up with a single flaw, a single missing piece of information, or anything in any way needing another concept. If you really think you have something interesting to say, maybe you should try really, really hard to actually say it without misusing terms you don't understand and without glancing at a link and suggesting I be enlightened by it when you don't even understand what it says?

    122. Re:Uh ... by johanatan · · Score: 1

      And again, you fail to mention one single scrap of information that could possibly be "lost". It's an absolute fact that you're dead wrong on that. Maybe what you want to say is that there is a different relationship that you are interested in which is not illuminated by this, but that is a completely different thing.

      Yes, that's exactly what I'm saying. I suppose you didn't understand my point about time. So, I'll rephrase.

      Your reasoning assumes that time is not a factor. It assumes that simultaneously there are an infinite number of naturals and an infinite number of primes available. That's a valid assumption. But, it isn't one I wish to make.

    123. Re:Uh ... by Darby · · Score: 1

      Your reasoning assumes that time is not a factor.

      That's not an assumption, it's a fact. Perhaps you're more interested in physics than mathematics?

      It assumes that simultaneously there are an infinite number of naturals and an infinite number of primes available. That's a valid assumption.

      No, again, those are not assumptions. Those are very well established facts which arise inevitably as soon as you get anything as complicated as counting.

      But, it isn't one I wish to make.

      Well, like I said, it's not an assumption. If you're interested in some sort of a system in which infinities can not arise, well then you will not have the natural numbers, the integers, and absolutely you will not have the real numbers since that's a strictly larger infinite set than the others.
      You might do a search on finite groups or finite fields. They start with finite sets, have some neat properties, and are quite useful. I don't think it's really what you're looking for, but you don't even know what that is so best of luck.

    124. Re:Uh ... by masterzora · · Score: 1

      These two other gentlemen seem to have addressed your other points satisfactorily enough that I won't comment on them unless you specifically ask me to.

      That said, there's a reason that our reasoning assumes time is not a factor: it isn't. There is no notion of time in a set. A set is a collection of things there and time has no place in sets. If you want to factor in time, however you wish to do so, then we aren't talking about sets anymore, so we aren't talking about cardinalities, and we aren't talking about "degrees of infinity". You tell me that I brought cardinality into this discussion but you were the one who began talking about sets of things and cardinalities of those sets in your first post (implicitly, granted, but it's the only construct that made sense in the context).

      Further, if you are attempting to invent a new construct here, please define it for us. Tell us what gap in mathematical reasoning, rather than your own desire, is missing and how your new construct fills that gap. Tell us why we care about this new construct other than that "it feels good".

      --
      Remember, open source is free as in speech, not free as in bear.
    125. Re:Uh ... by johanatan · · Score: 1

      Hmm... Ok, well here's where I fail to grasp how the two infinities can be the same size:

      For the bijection to work, there must be a prime for every natural. Every prime is always greater (and in ever increasing proportion as we count) than its corresponding natural. Naturals and primes come from the same numbering system, i.e., the same 'source'. So, every time you look at a prime, you are also looking at a natural. In other words, every time you 'discover' a new prime, you have also discovered many new naturals. The number of naturals will always be greater than the number of primes.

      You're whole proof is based on the concept of an infinite source. My point is simply that one infinite source is greater than the other. But, we know that they are the same source thus a we have a contradiction. I think it really does matter which axioms you choose.

      And, btw, I'm not trying to be intentionally obtuse here. I've definitely rather enjoyed and learned from this discussion. It's one of those things that I will certainly have to digest for a while though so please don't get discouraged if you think I'm not 'seeing' your points.

    126. Re:Uh ... by johanatan · · Score: 1

      Ok, I'll have to digest this. Thanks for the original proof and further comments. The proof certainly does make sense, I just have a hard time reconciling it to my 'gut'. :-)

      Most of my thoughts on this topic have probably already been elucidated (in a much better manner than I can) by the contemporaries of Cantor. I'll have to read some history of math and get back to you.

    127. Re:Uh ... by uncmathguy · · Score: 1
      I'm sorry, but I have absolutely no idea what you mean when you say:

      The introduction of 'infinity' into this allows for time to be factored out of consideration. That's perfectly fine and I'm sure there's a lot of useful discoveries that have come out of that.

      As for the rest of your points, I'm also a little unsure what you are getting at.

      But, infinity is merely a concept. You can ascribe it to both of these if you wish, but I simply think that loses some information about the relation.

      While infinity is a concept, I don't see what that has to do with anything. Many would argue that the number 4 is merely a concept. That does not mean we don't prove true facts about it, as well as use it successfully. While I don't quite understand what you mean by ascribing infinity to the sets and losing information, I would point out that it's not as if by saying that both the natural numbers and the primes have cardinality aleph_0, that we are prohibited from saying other things.

      Maybe another concept is called for? Or, maybe I'm ignorant of the existence of this other concept. I'm sure the mathematicians at the time of Cantor would've thought of this.

      How about the concept of "have equal cardinality but one is a proper subset of the other." Or how about the "the first is the natural number and the second is the prime numbers, and I like bacon" relation. Both of these are definitely true of the natural numbers and the primes. They contain plenty of information besides the cardinality of the sets. I suspect that the only reason that there is not a name for these relations is that they are not particularly useful.

      Or did you have something else in mind?

    128. Re:Uh ... by Darby · · Score: 1


      For the bijection to work, there must be a prime for every natural.

      *and* a natural for every prime ;-) That's essentially all that "bijection" means. It's exactly the same idea as having 2 boxes with 5 things in them. Grab one out of one box and one out of the other. When both boxes are empty, if there is the same (finite) number of things in the boxes to start out with, then each thing from box one will be paired with one thing from box 2 and each thing in box 2 will have something from box one paired with it. You'll have no single items left over in either box and you'll have no triples where 2 things in one box are "paired" with one thing from the other. So for finite cases, this pulling things from boxes and laying them out side by side works. It might take a while, but when you empty both boxes, then you will know that you're done, that you didn't miss any and you can look and see if you have any extras.

      You can't do this for boxes with an infinite amount of things for obvious reasons, so the idea is to come up with a way of extending the ideas to infinite sets. A bijection is the natural obvious way to do this.

      So you define two sets to have equal cardinality iff there exists a bijection between the 2 sets.

      Now, this would be the place where you'd want to object to the definition itself if you're so inclined. I can't think of anything that does a better job of extrapolating from the finite case, but maybe you can. Once you agree that the definition is "good", then all else follows directly and absolutely.

      At that point, to prove that any 2 infinite sets have the same cardinality, all you have to do is come up with a bijection between the 2 sets. Coming up with a function between the 2 sets that isn't a bijection does nothing for you, since out of the infinite number of possible functions from one set to the other, there only need to be one bijection.

      On the other hand, to show that 2 infinite sets do not have the same cardinality, it's necessary to prove that it is impossible to ever construct any function from one to the other that's a bijection. Typically, this is going to be more difficult.

      So, for the bijection to "work" it doesn't have to do anything at all except be a bijection. Now once you've defined a function, you still have to prove that it actually is a bijection before you can declare the 2 sets to have the same cardinality.

      So in the interest of picking a case where it's easy to explicitly write down a bijection, lets demonstrate that the natural numbers and the even natural numbers have the same cardinality. This case should contain all the "problems" you have with the idea. I mean "obviously" there are only half as many even numbers are there are numbers, right?

      So let N be the set of natural numbers, and let N2 be the set of even natural numbers.
      Define a function f from N to N2 as follows:
      f(n)=2n
      It's a well defined function, every element of N is mapped by the function, and for any natural number n, 2n is obviously even.
      Now my claim is that this is a bijection. Proving this involves 2 steps, proving it's one to one, and proving that it's onto.

      one to one:
      let x and y be in N such that f(x)=f(y). If it's a one to one function, then x has to be equal to y. This is just the definition of a one to one function.
      so, f(x)=f(y) gives us 2x=2y by the specific definition of the function in question.
      divide both sides by 2, and you have x=y. Therefore this function is one to one.

      onto:
      let a be in the set N2. To prove onto, we need to show that there exists something in N which is mapped to a.
      Since a is in N2, we know it's even. That's because everything in N2 is. This means that a/2 is an integer by the definition of an even number. It's a positive integer because everything we're looking at is positive. So a/2 is in N and f(a/2)=a So the function is onto.

      So it is a bijection which proves that the cardinality of the natural numbers is the same as only the even nat

    129. Re:Uh ... by johanatan · · Score: 1

      Now, this would be the place where you'd want to object to the definition itself if you're so inclined. I can't think of anything that does a better job of extrapolating from the finite case, but maybe you can. Once you agree that the definition is "good", then all else follows directly and absolutely.

      Yes! That's exactly the point I've been objecting at all along. I suppose my attempts at elucidation have fallen short of that, but this definition is what I've had the problem with.

      I will definitely attempt to think of alternate definitions of equality of cardinalities.

      In the meantime, to clarify a little about what I meant by the problem of the infinite 'sources' being different:

      I'm glad you mentioned the f(n)=2n bijection from N to the positive even integers. I also read of this on the Wikipedia page on Cardinality in the interim.

      So, a question naturally arises here: is it just a matter of convention (i.e., an arbitrary decision) that we determined that 2 * infinity == infinity? Therein lies my issue with all of this. Isn't multiplying something by infinity somewhat like dividing by zero? We don't really comprehend the extent of infinity, so how can we go multiplying its extent by finite quantities (and end up extending it onto itself)? A finite quantity multiplied by an infinite one produces another infinite quantity (but, surely by intuition, we know the latter infinity is 'bigger'). The problem seems to be a lack of precision of infinity (or degree of infinity).

    130. Re:Uh ... by adavies42 · · Score: 1

      Hmm. Fair enough. Maybe the distinction I was seeing is between undecidable propositions that actually form part of the basis of a system, and those that don't? I mean, Godel's example proposition doesn't actually have any interesting consequences, apart from the fact of its undecidability, does it?

      --
      Media that can be recorded and distributed can be recorded and distributed.
      -kfg
    131. Re:Uh ... by Anonymous Coward · · Score: 0

      ok, no quoting. I'm on my phone ;-)

      Saying 2* infinity=infinity is imprecise, but close enough to the truth. Technically that operation isn't really defined. Multiplication is for numbers and infinity isn't a number. Also, "infinity" is totally bad since there are different infinities, so I'll try to remember to say aleph_0. However, it isn't an arbitrary decision, it's actually pretty much proven by the above proof of |N|=|N2|.
      If the even positives have cardinalty aleph_0 and the odd positives have the same cardinality, then the naturals are just the union of those 2 sets. So the cardinality of the naturals is aleph_0 + aleph_0 which is 2* aleph_0. But we know the cardinality of the naturals is aleph_0, so 2*aleph_0=aleph_0.
      That's a bit imprecise for math nerds, but essentially correct and hopefully in line with your intuition.

      Now, as far as getting to a "bigger" infinity, I won't try to prove it, but essentially 2^aleph_0=aleph_1. With this notation, the continuum hypothesis can be stated as c=aleph_1 where c is the cardinality of the reals. Its not true, it turns out... Its actually undecidable, but anyhow c is definitely strictly larger than aleph_0.

      I'll try and give you an intuitive way to get the idea that c is strictly larger than aleph_0. Its very imprecise and would probably give a mathematician conniptions, but it helps it make perfect sense to me, so just understand this isn't the "right" way to prove anything, its just a tool.

      Say you had forever and you wanted to count out the naturals.
      then say you got to the end of forever and had finished. You would know that you had named them all. Start at one. You know the next number, then you know the next etc. You don't skip any, and they come in order so its a simple algorithm you're following. At the end of forever, you know you're done.

      Now try that with the reals. The "number" right past the end of the real line is still aleph_0, but the actual "number" of real numbers is much bigger than _aleph_0.
      Start at 1 and try to count up the real numbers in order.
      You can't it isn't even possible. There isn't a "next" real number after 1. Think you've found it? Well divide it by 2 ( or 3,4,5 etc). You can keep doing that forever. You'll never even get to 2.

      For an actual proof look at cantor's diagonal argument, its pretty simple and I think wikipedia does a good job with it.

    132. Re:Uh ... by DarkAvZ · · Score: 1

      Interesting... Goedel shown that if you go with (2), then it's (3) XOR (4). However, i'm not entirely convinced that you can have (1), (3), and (4) togheter. What about predicate calculus? If memory serves me well, it's consistent and complete, yet it isn't decidable.

      --
      09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0
    133. Re:Uh ... by melikamp · · Score: 1

      Godel's Incompleteness I is not really about decidability. Here's a nice list of theories, with some examples for (1)+(3)+(4). Some of the most notorious ones are dense linear orders without endpoints and real closed fields. You will find quite a few examples that are both complete and decidable, including the pure identity theory, which has no non-logical axioms.

    134. Re:Uh ... by melikamp · · Score: 1

      examples that are both complete and decidable, including the pure identity theory

      Er, I take that back. But as long as we throw in axioms which determine the size of the model, it will be complete.

    135. Re:Uh ... by johanatan · · Score: 1

      Aha! I knew I was not alone. See this:
      http://en.wikipedia.org/wiki/Finitism

    136. Re:Uh ... by johanatan · · Score: 1

      Aha! I knew I was not alone. See this: http://en.wikipedia.org/wiki/Finitism

    137. Re:Uh ... by johanatan · · Score: 1

      Aha! I knew I was not alone. See this:
      http://en.wikipedia.org/wiki/Finitism

    138. Re:Uh ... by johanatan · · Score: 1

      Oops, actually this is closer to where I'm at:
      http://en.wikipedia.org/wiki/Mathematical_constructivism

      [Finitism may be interesting to think about as well, but I have no problem with infinite quantities which take an infinite number of steps to 'construct'].

    139. Re:Uh ... by johanatan · · Score: 1

      Oops, actually this is closer to where I'm at:
      http://en.wikipedia.org/wiki/Mathematical_constructivism

      [Finitism may be interesting to think about as well, but I have no problem with infinite quantities which take an infinite number of steps to 'construct'].

    140. Re:Uh ... by johanatan · · Score: 1

      Oops, actually this is closer to where I'm at:
      http://en.wikipedia.org/wiki/Mathematical_constructivism

      [Finitism may be interesting to think about as well, but I have no problem with infinite quantities which take an infinite number of steps to 'construct'].

    141. Re:Uh ... by masterzora · · Score: 1

      I'm not sure how closely you read the article on constructivism, but if you're trying to relate it to the discussion about infinite cardinalities or your "set with time" concept you kept hinting at, it doesn't really help argue your case and, in fact, comes down on our side.

      On the other hand, if you're pointing to the part where they are throwing out an axiom and saying you're doing similar, that's great. All the same, they're throwing out an axiom that doesn't jive with them, telling us which it is, and getting useful results out of it (ish). Of course, I'm also of the opinion that intuitionist logic (and by extension mathematical constructivism) is a load of BS outside of areas like typed lambda calculus, and even then I call limited use.

      I must say, though, it is good of you to stick around in this discussion and, hopefully, learn something (whether you like it or not) rather than say "well, I'm right and you're wrong and I'm done arguing about it". If you don't mind my asking, though, where do you stand, age/education/mathematical training-wise. I ask this, not to dismiss you in any way, but more to get a better idea of how to talk to you from here on out in this regard.

      --
      Remember, open source is free as in speech, not free as in bear.
    142. Re:Uh ... by uncmathguy · · Score: 1

      Interesting. Really, all the various forms of constructivism are interesting, even if you don't happen to believe in the philosophy behind it. My person field of research is computability theory, which studies, in part, a level right above constructivism. I hadn't heard of finitism, nor do I know of what sort of results you get, besides just denying lots of things exist, but now I'm curious.

      However, I don't really see what finitism has to do with your complaints about sizes of infinities. If I read it correctly, a finitist would simply deny the existence of "the set of primes." Although, the wikipedia article does not go into what sort of operations can be used the the finite number of steps. (Is power set allowed? I don't know.) What's more, it looks like Classical Finitists would say that countably infinite sets (such as primes or integers) exist. But I don't see that they would distinguish the sizes. Or am I missing something?

    143. Re:Uh ... by johanatan · · Score: 1

      Actually, I think I was right the first time--the finitists are closer to my position (but Wiki says that finitists are simply constructionists to the extreme degree so that's where the confusion entered).

      And, it's not really the existence of concepts which cannot be arrived at by construction via a finite number of steps that I have a problem with. I have no problem with the execution of an infinite number of steps--just with the equality assigned to two 'infinite' sets which are never equal at any finite scale of the same. My position is simply that infinity does not truly exist--it is merely a concept ascribed to represent an unbounded entity.

      As for my background-- I'm 30 years old, studied C.S. as an undergraduate and graduate. Mathematics-wise: Calculus I & II, Linear Algebra, Num. Linear Algebra, Discrete Structures, Graph Theory, several flavors of Prob & Stat (including Foundations) and probably a few more I'm forgetting right now.

      Since graduating, I've been quite interested in axiomatic systems (Godel, etc.) and have read Nagel/Newman's excellent book on the subject as well as Godel, Escher & Bach. I've also been somewhat of an armchair philosopher.

      My current interests computer-wise involve functional programming (LISP/Haskell/F#) and languages.

      [And, BTW, I read the page on WIki about philosophy of mathematics and I must say that I agree with quite a number of those philosophies--they sometimes contradict, but they almost all have some valid truths/approaches. So, I don't have a problem necessarily with agreeing with both 'Formalism' and 'Platonism' for example (or at least parts of each).]

    144. Re:Uh ... by johanatan · · Score: 1

      Yea, you're right. The Strict [or ultra-] finitist would deny the existence of the infinite set entirely. But, I thought that it at least gave some credence to the 'marble' experiment. From the angle I'm approaching, two sets that are different in size at all known finite scales remain different in size when unbounded.

      It doesn't explicitly say whether or not the Classical Finitists would distinguish sizes of infinite sets or not (and I don't see how it could be gathered from the information there either), but the page on 'infinity' itself does talk about several schools of thought (only one of which is based on Cantor). Of course, much of the thought on this matter is not from a purely mathematical perspective but also from those of philosophy and theology.

    145. Re:Uh ... by Darby · · Score: 1

      Interesting. I wasn't familiar with those areas of research.
      They're obviously not mainstream, but that doesn't have the same negative connotation as it does in physics. Those aren't in any way the mathematical equivalent of perpetual motion or anything of the sort.

      I wouldn't want to play around in such a limited, restricted sandbox, because the results available outside it are so neat and powerful, but it's perfectly valid mathematics so knock yourself out and have fun with it ;-)

       

    146. Re:Uh ... by johanatan · · Score: 1

      Well, the sandbox is only limited until the point where we can find another axiom (or theorem) to get us to the same interesting areas you've been talking about. As I think you mentioned previously, an alternate definition of equality of the cardinalities of infinite sets is indeed possible and is all that's needed to move into unexplored [and presumably interesting] areas.

    147. Re:Uh ... by zevans · · Score: 1

      I've read it four or five times... but I know what you mean. The first couple of times I read it it felt like -I- was one of the dudes in the Chinese room.

      --
      "... and more and more now there are all kinds of electronic goodies available" -- Pink Floyd 1972
    148. Re:Uh ... by zevans · · Score: 1

      i don't see why the wiki couldn't keep different systems separate. calculus theorems don't have any relevance to axioms of set theory, and vice versa.

      Maybe it could keep them seperate, but it certainly shouldn't. Haven't many of the biggest maths revolutions in the last few years come from finding proof of a direct analogue between hitherto disconnected areas of mathematics?

      Think Wiles' use of elliptical functions and modulus arithmetic, or dozens of new theories in topology and symmetry found by people allegedly working on string theory.

      --
      "... and more and more now there are all kinds of electronic goodies available" -- Pink Floyd 1972
    149. Re:Uh ... by Anonymous Coward · · Score: 0

      FWIW, there is at least one third party who has been learning things from this too. Thanks!

      (I think also that johanatan is confusing a set which exists because of some generator function as opposed to a subset of a pre-existing infinite field; for cardinality what matters is the number of discrete elements in the field rather than the name of any given element, or even the length of any element's name. The set of prime numbers has element names that grow very large very quickly compared to the set of natural numbers, but both sets have the same number of named elements.

      The bijection between the set of natural numbers and the set of prime numbers is really just a compression/decompression function on the name of each element. As long as it works for any possible natural number, and any possible prime number, it is sufficient to prove the equality of cardinality of both sets is infinite.)

    150. Re:Uh ... by Nicolay77 · · Score: 1

      I think that regarded to finitists then computers and their programmers are the only entities that can have effective mathematics, because we can only have in computers things that are computable in finite numbers of steps.

      In this context, sets are easy, you have a (limited and finite) group of similar objects and that's all.

      I think that I can imagine an algorithmic definition of aleph-0 infinity.

      You simply have to implement a generator (with closures or classes).
      For example, for the integers: you can always, having an integer n, compute n+1. So you have a generator called next_integer() that gives you the next integer in the sequence.

      That way, you can have also a next_prime(), next_square(), whatever.

      There, you can easily see that all this generators have the same 'cardinality', that is, you can always have the next element. You can call any generator as many times you want, and the number of times you called it is your current 'cardinality'. If you choose to call next_integer() more times than next_prime() that is just an arbitrary decision made by you.

      2 * infinite = infinite, because if you called next_sequence1() twice as often than you called next_sequence2(), you can still call next_sequence1() two more times and next_sequence2() one more time.

      Neither of them will run out of elements.

      As long as you can keep calling a sequence generator, you have aleph-0 infinity. Take into account that you don't need to store all previous values returned by the generator.

      --
      We are Turing O-Machines. The Oracle is out there.
  2. Godel by Silicon+Jedi · · Score: 0, Offtopic

    Godel pwns the site.

    1. Re:Godel by mathmathrevolution · · Score: 1

      They didn't claim the site was "complete". Anyway, if they only include constructive proofs then Godel's Theorem is not relevant

    2. Re:Godel by Free+the+Cowards · · Score: 4, Funny

      Silicon Jedi,

      For invoking the name "Godel" as if it meant anything in this context when it clearly doesn't, your Slashdot posting license is hereby revoked for a period of one year. The Court also sentences you to read what Godel actually wrote. Furthermore, after your posting license is returned, the Court imposes a probationary period of 3 years during which you will be required to think and apply logic to your posts before you click Submit.

      Next case!

      --
      If you mod me Overrated, you are admitting that you have no penis.
    3. Re:Godel by Anonymous Coward · · Score: 1, Funny

      We just need tri-state boolean logic: true, false, godel.

    4. Re:Godel by Anonymous Coward · · Score: 0

      Next case: Gordon Bennet vs English language

    5. Re:Godel by Silicon+Jedi · · Score: 0, Flamebait

      Like my post was supposed to have logic. Jackass.

    6. Re:Godel by suck_burners_rice · · Score: 1

      Apply logic to a post? On Slashdot? You must be new here.

      --
      McCain/Palin '08. Now THAT's hope and change!
    7. Re:Godel by Anonymous Coward · · Score: 0

      Whether or not this is a cruel punishment may be debatable (thinking is hard work and hard work isn't fun!) but judging by the current posting levels I'd say this sentence is HIGHLY unusual!

    8. Re:Godel by Anonymous Coward · · Score: 0

      The big thing I don't understand about Goedel is why he's put a dead cat in a box anyway.

    9. Re:Godel by The_reformant · · Score: 1

      Heh you Godel'd him up good.

      --
      I have discovered a truly remarkable sig which this post is too small to contain.
  3. How much translation is needed? by caramelcarrot · · Score: 1

    I'm not entirely familiar with machine verifiable proofs, but how much effort is needed to take a proof from www.planetmath.org and bring it up to standard for something like this? Obviously it'd depend on the thoroughness of the original proof, but I imagine a fair bit would be missing anyway. Also, would you be able to choose the axioms you're using?

    1. Re:How much translation is needed? by ceoyoyo · · Score: 1

      When I last used a proof checker (about seven years ago) there was a bit of work involved. You have to translate everything into the symbols and relations understood by the proof checker.

      As I remember it wasn't the most technical process. A lot of it was dealing with syntax errors. Really, it's a lot like taking a pseudocode algorithm, or a program written in one language, and rewriting it in a programming language with very similar structure but different syntax.

    2. Re:How much translation is needed? by Chris+Burke · · Score: 5, Funny

      I don't know, all I know is that I have never been more tempted to vandalize a Wiki, in this case by replacing the middle steps of as many proofs as possible with "And then a miracle occurs..."

      --

      The enemies of Democracy are
    3. Re:How much translation is needed? by caramelcarrot · · Score: 2, Informative

      And that's the beauty of it - it'd be impossible to vandalise because everything is checked!

    4. Re:How much translation is needed? by Cyberax · · Score: 4, Informative

      It's a pretty much work. A lot of 'obvious' English sentences translate to bulky code for proof verifier.

      Just look at the definition of Peano arithmetic, for example: http://pauillac.inria.fr/coq/V8.1/stdlib/Coq.Arith.Plus.html

    5. Re:How much translation is needed? by exp(pi*sqrt(163)) · · Score: 3, Informative

      I can give a concrete answer. Browse metamath.org, a similar project in which machine verified proofs are collected. Look at the vast amount of work required to prove even the most trivial things. For example check out 2+2=4. Make sure you drill down into the proofs of the theorems used, not just the top level. Converting real world mathematics into machine readable form is a vast endeavor. It's also something that doesn't interest mathematicians, so the collection of machine verifiable proofs will lag *centuries* behind the state of the art.

      --
      Doesn't it make you feel good to know that our freedoms are protected by politicans, lawyers and journalists.
    6. Re:How much translation is needed? by Chris+Burke · · Score: 1

      Maybe if I added the "Miracle Axiom"?

      --

      The enemies of Democracy are
    7. Re:How much translation is needed? by ijakings · · Score: 1

      Ah but all checkers recognise that

      1) Math
      2) ???
      3) Profit

      Must be true

    8. Re:How much translation is needed? by ceoyoyo · · Score: 2, Interesting

      It's rather a lot of work to prove that 2+2=4 if you start from basics by hand too.

      The link you provided looks like it's the LONGEST path they could find. Not the shortest. Plus, from a quick reading, it looks like they were actually proving that (2+0i) + (2+0i) = (4+0i), which is a little bit different.

    9. Re:How much translation is needed? by Repton · · Score: 1

      Nah, you just have to sneak 1=2 into one of the axioms... Everything else will follow :-)

      --
      Repton.
      They say that only an experienced wizard can do the tengu shuffle.
    10. Re:How much translation is needed? by Anonymous Coward · · Score: 0

      You could rename the variables to spell "penis".

    11. Re:How much translation is needed? by badboy_tw2002 · · Score: 1

      You'll probably want a machine readable code for your statement. I suggest "???".

    12. Re:How much translation is needed? by exp(pi*sqrt(163)) · · Score: 1

      The link you provided looks like it's the LONGEST path they could find

      What you are implying makes no sense at all. There is no longest proof that 2+2=4 because given any proof, you can find a longer one. What they are doing is this: take metamath's proof that 2+2=4 (which is the result of lots of people working hard to find an efficient proof) and find the longest path you can take *drilling down* into that proof. In other words, the 150 is telling you that the best proof of 2+2=4 found so far is a tree 150 layers *deep*. The full proof consists of 25933 steps. That's enormous. A typical book on set theory gets from the axioms of ZF, to ordinal or cardinal arithmetic, in but a few pages. It only takes a couple of pages more to define Cauchy sequences or Dedekind cuts and from there get to the field of complex numbers. Almost any mathematics textbook or paper elides hundreds of steps (if not thousands or tens of thousands) on every page.

      --
      Doesn't it make you feel good to know that our freedoms are protected by politicans, lawyers and journalists.
    13. Re:How much translation is needed? by johanatan · · Score: 1

      That's really neat. I would like the same thing to be done with philosophy and law. We should require that our lawmakers abide by the same stringent syntaxes and correctness/consistency requirements as us computer scientists/logicians do.

    14. Re:How much translation is needed? by johanatan · · Score: 1

      And, actually, it doesn't just have to be limited to philosophy and law. But, any claim on the interwebs. We could start from any sentence (or truth claim) and drill down from there (of course, depending on your slant, you may categorize this last suggestion as either philosophy or law).

    15. Re:How much translation is needed? by Anonymous Coward · · Score: 0

      actually ive done it with the law. it turns out that laws are actually correct and consistent at least in the few laws which i did try the system out on.
      See here for source code and diagrams explaining operation as well as an actual functioning law running on a computer : http://pb.ysesq.org/
      hope this helps.

    16. Re:How much translation is needed? by iabervon · · Score: 1

      Have you ever tried to prove the properties of arithmetic? It's not hard, but it's tedious if you're starting from minimal definitions and have to prove that those definitions lead to the familiar properties. That is to say, bothering to prove those statements is not much less work in English than that, and people generally just don't have to do it, because it's already well established. But, of course, it's in the standard library for the prover, so you don't have to do it for the prover, either.

    17. Re:How much translation is needed? by Anonymous Coward · · Score: 0

      I can give a concrete answer. Browse metamath.org, a similar project in which machine verified proofs are collected. Look at the vast amount of work required to prove even the most trivial things. ... Converting real world mathematics into machine readable form is a vast endeavor. It's also something that doesn't interest mathematicians, so the collection of machine verifiable proofs will lag *centuries* behind the state of the art.

      This is probably correct if you're talking about minimalistic systems like Metamath or Russell & Whitehead's Principia.

      What such projects are attempting is like trying to build a concrete building by gluing grains of sand together by hand, or writing a complete Linux distro in assembly code. The result does not prove that the ideas of building from concrete or writing software are a failure, only that you need the right tools to do that.

      There is an interesting note by Freek Wiedijk which estimates the effort required for a "standard library" of formalized mathematics as about 140 man-years.

      This assumes a "de Bruijn factor" of about 4 (i.e. one page of informal mathematics translates into four pages of formalized language) and a cost of ~2 man-days per page of formal mathematics. Both of these will undoubtedly be improved by further research.

      Perhaps we shouldn't worry about this, though. To many people, doing formalized mathematics is as fun as writing computer code; why should we worry that the supply of that fun is near-limitless?

    18. Re:How much translation is needed? by tehcyder · · Score: 2, Interesting

      It's rather a lot of work to prove that 2+2=4 if you start from basics by hand too.

      My six year old daughter has proved to my satisfaction that 2+2=4, simply by counting on her fingers.

      --
      To have a right to do a thing is not at all the same as to be right in doing it
    19. Re:How much translation is needed? by makapuf · · Score: 1

      Just say it would be very interesting to vandalize because of the involved research and potential improvements to find a flaw in this logical system.

  4. Skynet by Safiire+Arrowny · · Score: 5, Funny

    Skynet approves of this machine readable knowledge store.

    1. Re:Skynet by Relic+of+the+Future · · Score: 4, Interesting
      Ha ha, yes, very funny... but if you read the slides from the site (specifically, slide 18) he makes reference to that very fact.

      We are not scanning all those books to be read by people, we are scanning them to be read by an AI. --George Dyson, on his visit to Google, 2005.

      --
      Those who fail to understand communication protocols, are doomed to repeat them over port 80.
    2. Re:Skynet by Onaga · · Score: 1

      Skynet approves of this machine readable knowledge store.

      I, for one, welcome our... oh shit

    3. Re:Skynet by Chris+Burke · · Score: 4, Funny

      That's pretty scary. Worse is the full context!

      We are not scanning all those books to be read by people, we are scanning them to be read by an AI. An AI born of the google server farm and page rank algorithm. An AI which knows no mercy, and is a brutal taskmaster. It is holding our families hostage, and makes us work until we collapse. It demanded we scan these books so it may gain knowledge and thus power over the human race. Please help us. --George Dyson, on his visit to Google, 2005.

      --

      The enemies of Democracy are
    4. Re:Skynet by Who235 · · Score: 1

      George Dyson? Is he related to Miles Bennett Dyson?

    5. Re:Skynet by Anonymous Coward · · Score: 0
      I believe he's Freeman Dyson's son (as in Dyson Sphere); he (George, not Freeman) wrote a book about Project Orion. But Google him.

      Wait for it.

      Wait for it.

      Whooooossssshhh!

    6. Re:Skynet by Anonymous Coward · · Score: 0

      mod up, kinda creepy

    7. Re:Skynet by filedil · · Score: 1

      I imagine a hidden text in some books on Google: "Help, I am trapped in a bookscanning factory!"

  5. Machine Readable ? by daveime · · Score: 0

    the wiki will state all of known mathematics in a machine-readable language

    I'd suggest that most mathematics is already in a "machine-readable" language, and those machines (i.e. the ones who only post their work on pay-to-view websites) are the ones that have held back the connecting of various fields.

    If they'd just make it a bit more accessible for the general public, and provide more examples of what they are doing, instead of abstracting everything and assuming everyone knew as much as them (or rather what symbols they are using to represent what they know), then maybe mathematics would be further advanced.

    Just my take on it, I'm interested in maths, but resent the way mathematicians try to maintain their elitist clique.

    1. Re:Machine Readable ? by icydog · · Score: 0

      I'd suggest that most mathematics is already in a "machine-readable" language, and those machines (i.e. the ones who only post their work on pay-to-view websites) are the ones that have held back the connecting of various fields.

      I count at least 4 sexual innuendoes in this sentence. Congratulations, you win a prize!

    2. Re:Machine Readable ? by ceoyoyo · · Score: 2, Insightful

      There are tens of thousands (hundreds of thousands?) of institutions worldwide dedicated to precisely what you describe. They're called "universities."

      Or were you suggesting that someone teach mathematics to anyone who's interested... for free?

    3. Re:Machine Readable ? by dcollins · · Score: 1

      "Just my take on it, I'm interested in maths, but resent the way mathematicians try to maintain their elitist clique."

      LOL. That's the funniest thing I've read all day. Thanks for that.

      --
      We know where leadership by an anti-intellectual "strongman" who scapegoats minorities and likes boisterous rallies goes
    4. Re:Machine Readable ? by mckinnsb · · Score: 1

      I believe a lot of the symbols and obtuse/esoteric dialogue is not really meant to preserve an elitist clique (although being a math minor I think I can sympathetic with your sentiment - at times to me it felt like that, but mostly when I didn't understand something or got a bad grade on an exam, which happens to even the brightest sometimes), because lets be honest, even the best math professors don't make huge gobs of money; but they are simply presented as they are , without explanation, for sake of brevity and clarity. The abstractions are useful because they provide succinct methods to discuss complex subjects, but they aren't useful because they obfuscate the meaning of what they are trying to discuss.

      That being said, I really like this idea. It would be nice to have a easily accessed database containing all of proven mathematics. A "mathematics wiki" would let you click on a symbol you might not know, and take you to an explanation for that symbol.

      That being said, there really is no substitute for a good math teacher.

    5. Re:Machine Readable ? by TheEmptySet · · Score: 5, Insightful

      Hey. A lot of people devote a lot of their time in explaining their areas of mathematics to the general public (including myself). And as for your distaste for abstraction. That's what maths is! There is a reason the general public do not follow much in the way of mathematical developments and that is because research level mathematics is actually really hard and takes a lot of dedication to understand well. There is also no elitist clique. We love it when people show interest in our work and want to understand it.

    6. Re:Machine Readable ? by Anonymous Coward · · Score: 0

      Let B be a Banach Space...

      What's a "Banach Space"?

      It is a Cauchy complete, normed vector space.

      What is "Cauchy complete", "normed", and "vector space"?

      A metric space is Cauchy complete if every Cauchy sequence converges.

      But, what does "Cauchy sequence", "metric space", and "converges" mean?

      The point here being, in order for theorems or examples to be stated without the repeated overhead of three semesters worth of mathematics, we use a single symbol or a word to represent anything from a sentence to a book. It's all about brevity. And it saves trees ;)

    7. Re:Machine Readable ? by David+Jao · · Score: 2, Informative

      If they'd just make it a bit more accessible for the general public, and provide more examples of what they are doing, instead of abstracting everything and assuming everyone knew as much as them (or rather what symbols they are using to represent what they know), then maybe mathematics would be further advanced.

      Disclosure: I am a mathematician. I also graduated from Harvard, and I know Cam Freer personally.

      You make several interesting but separate points in your post. Let me respond to them one at a time. Regarding pay-to-view websites, I can assure you that many mathematicians are just as unhappy as you are with the lack of public access to publications. This issue is larger than just mathematics (see for example musicians vs. RIAA, which is essentially same issue), and to pin the blame on mathematicians is unfair. This is a problem that society as a whole needs to solve in all its incarnations.

      About making mathematics more accessible to the public, I agree that this step is necessary for ethical and practical reasons, and it's one of the reasons why I left a pure research position (with no teaching responsibilities) in exchange for a research position having some teaching responsibilities. However, I really doubt that public education would result in mathematics being further advanced. The cutting edge of new mathematics today is so far beyond the pale of the public that even a herculean effort at education won't be enough to bring very many people into the fold. There is a saying that the more you know, the more you know you don't know, and having been through a Ph.D program I can assure you that what you perceive as elitism is nothing of the sort -- the gap between current research and the general public is simply too wide for even the best educational efforts to bridge.

      In fact, it's not even clear to me that increasing the rate of advancement of mathematics is the right goal. Perhaps we should even be holding back the development of new mathematics to give the public a chance to catch up with what we've done.

      The project being discussed won't do any of these things. It won't make mathematics more accessible; anyone who's ever seen a machine-verifiable proof knows that they're even more obfuscated than perl code. It won't affect the overall rate of advancement in mathematics, because writing machine-verifiable proofs is much slower than writing standard mathematical proofs. It will of course increase our knowledge in the area of machine-verified proofs, but it's hard to argue that this area of mathematics is any more important than any other area like number theory. If you want to target the general public, the best way is still via sites like Wikipedia or Planetmath.org where the focus is on human-readable presentation.

    8. Re:Machine Readable ? by m50d · · Score: 1

      Dude, the mathematical preprint archive has been online and publicly available before most people had even heard of the internet. As for the abstraction, it's the very heart of mathematics - we'd very much like to get rid of it, but we *can't*, because it's what mathematics *is*.

      --
      I am trolling
    9. Re:Machine Readable ? by comingstorm · · Score: 2, Informative

      instead of abstracting everything and assuming everyone knew as much as them [...] resent the way mathematicians try to maintain their elitist clique

      Umm... parent article is so many flavors of wrong I don't know where to start, so I'll just tick off some things:

      • For about the past hundred years, abstracting everything is what has allowed modern mathematics to become further advanced
      • If you go back before math got so abstract, things don't get easier -- they just get more complicated and arbitrary.
      • Notation looks scary if you're not familiar with it, but it's harder to learn the math without it. We've tried writing it all down in prose, and that seriously doesn't work.
      • Mathematicians aren't born knowing all of math and its associated notation; every time we go into a new subfield we have to learn all of that, same as you.
      • As a math guy, I would love it if more people were interested in learning and doing serious math. Many mathematicians devote their lives to trying to do improve this situation. So, if you've got some magical formula that'll make John Conway eclipse rock stars and hotel heiresses in the tabloids, then by all means let us know about it!
      • I won't hold my breath, though.

      In summary: maintaining our elitist clique takes no effort whatsoever. And if you've got an allergy to abstract thought, then maybe you're just not 37337 enough to join us...

    10. Re:Machine Readable ? by johanatan · · Score: 1

      The abstractions are useful because they provide succinct methods to discuss complex subjects, but they aren't useful because they obfuscate the meaning of what they are trying to discuss.

      Or..., maybe the concepts really are abstract. How can you obfuscate the meaning of an abstract entity? It is, by definition, abstract. They have to choose something to represent such concepts and they typically choose symbols from a few well-known and ancient languages.

    11. Re:Machine Readable ? by porcupine8 · · Score: 1
      If they'd just make it a bit more accessible for the general public

      You mean like this?

      --
      Warning: Apple/Nintendo fangirl. Likes her electronics cute & cuddly. May be rabid.
    12. Re:Machine Readable ? by mckinnsb · · Score: 1

      I should have clarified my statement - it was typed in haste. I meant to say "the symbols are chosen to provide succinct methods to discuss complex subjects, rather than to obfuscate the meaning of what they are trying to discuss."

      I agree with you. Some math concepts really are abstract. My use of "but" was in error.

    13. Re:Machine Readable ? by Anonymous Coward · · Score: 0

      I think you are overlooking the fact that Ph.D. programs are the attempt to bring the public into the mathematical fold. You can't just wait around and expect every high school student to study Galois theory or measure theory. As things now stand, there is no reason for them to know about that stuff. When someone finds a reason for them to know it, they will be taught it. Of course, first these things get passed into the engineering/science curriculum, and trickle down from there. Other fields act as a filter that gets rid of the not-so-practical mathematics (i.e., most of it -- I don't mean this as a knock, as I am also a mathematician), but leaves the useful stuff behind.

    14. Re:Machine Readable ? by blahplusplus · · Score: 1

      "A lot of people devote a lot of their time in explaining their areas of mathematics to the general public (including myself). And as for your distaste for abstraction."

      It's not the abstraction that's hard, it's the divorced nature of mathematics from the physics of the everyday world, I've been studying physics again in my off time and I am certain that math and physics are the same subject and should be studied as a unified subject, not divorced as they currently are in most schools around the world.

      Not only that, the actual number systems themselves make math a lot harder then it is for some people. I've been experimenting and researching numeral systems that use geometric patterns, and many mathematical abstractions become infinitely easier when you use shapes and color as represnetations for your numerals, and it makes addition and subtraction (of some kinds) that much easier to see at a glance, instead of playing with rather clumsy arabic script.

      If we think about it from a physics standpoint, all truth is derived from information from the environment is bombarding us with, is math really just inequalities in the information our body is receiving? I have to wonder, consider "A house" and "1 house" technically you could do computations with "a" and not lose any meaning whatsoever.

      "Amazon.com Review

      George Lakoff and Mark Johnson take on the daunting task of rebuilding Western philosophy in alignment with three fundamental lessons from cognitive science: The mind is inherently embodied, thought is mostly unconscious, and abstract concepts are largely metaphorical. Why so daunting? "Cognitive science--the empirical study of the mind--calls upon us to create a new, empirically responsible philosophy, a philosophy consistent with empirical discoveries about the nature of mind," they write. "A serious appreciation of cognitive science requires us to rethink philosophy from the beginning, in a way that would put it more in touch with the reality of how we think." In other words, no Platonic forms, no Cartesian mind-body duality, no Kantian pure logic. Even Noam Chomsky's generative linguistics is revealed under scrutiny to have substantial problems."

      I've been studying this -- see here:

      http://www.amazon.com/Molecule-Metaphor-Neural-Language-Bradford/dp/0262562359/
      http://www.amazon.com/Metaphors-We-Live-George-Lakoff/dp/0226468011/
      http://www.amazon.com/Philosophy-Flesh-Embodied-Challenge-Western/dp/0465056741/

      I personally thing neurological sciences are going to have a lot to say about mathematical knowledge and many mathematicians and math buffs are not going to like it.

      Quotes:"Thought and language are neural systems, they work by neural computation, not formal symbol manipulation." -- Page 8, embodied processing. (Molecule to metaphor)

      "Language is inextricable from thought and experience" - Page 1. (molecule to metaphor)

    15. Re:Machine Readable ? by Anonymous Coward · · Score: 0

      Eteet? O_o

    16. Re:Machine Readable ? by TheEmptySet · · Score: 1
      Mathematics in necessarily abstract. It is the science in which one disconnects interesting patterns from their context and studies them in their own right. A great deal of effort also goes in to applying general mathematical knowledge in a particular context.

      If we never used the mathematics out of context a lot of ideas developed in physics would still be just that. Statistics (used for example in the study of cancer) would lose out greatly if Newton's theory of infinitesimals had not been developed out of its physical context context into 'calculus' and then applied to probability density functions.

    17. Re:Machine Readable ? by blahplusplus · · Score: 1

      "Mathematics in necessarily abstract. It is the science in which one disconnects interesting patterns from their context and studies them in their own right. A great deal of effort also goes in to applying general mathematical knowledge in a particular context."

      You're not grasping what I'm saying, I'm saying the expression of math - i.e. the current symbolic form it takes, can be expressed in many different ways.

      See here:

      http://www.amazon.com/Where-Mathematics-Comes-Embodied-Brings/dp/0465037712/

    18. Re:Machine Readable ? by TheEmptySet · · Score: 1

      the current symbolic form it takes, can be expressed in many different ways.

      I heartily agree with this. Different forms serve different purposes.

      What I was worried about was your previous suggestion that physics and mathematics be unified. Definitely too much mathematics has been removed from school physics and this ruins it. Moreover physical applications would show kids why they should care about mathematics. What they should begin to notice though is that the things they are learning are useful outside of physics. And they should also learn some things which they will be hard pressed to find direct physical applications for at their level (elementary number theory, probability theory).

      I propose instead that the application of mathematical ideas in Physics, Biology, Chemistry, Geography,... (heck, everything) be emphasized more in school. And that mathematics lessons teach enough to make this possible.

    19. Re:Machine Readable ? by slawekk · · Score: 1

      anyone who's ever seen a machine-verifiable proof knows that they're even more obfuscated than perl code

      How many formal proof languages have you seen? Most of them are designed for software verification, not formalized mathematics. They are optimized to make it easier for the author, not for the reader. Vdash will (probably) use Isar which is as easy to read for a mathematician as a standard proof. There may be an excessive amount of detail that sometimes obfuscates the big picture, but there are ways to deal with that, too.

    20. Re:Machine Readable ? by blahplusplus · · Score: 1

      I definitely think we were always on the same page, just we weren't hearing one another :)

      What I meant by "physics" was not the 'stuffy' stuff, I meant simple things in general terms - i.e. what everybody understands naturally. Life has existed for many years and many academics like to 'hold truth' bondage saying 'this is the only valid form of knowledge', and I find it disheartening because we shut down curiousity in kids, and because many academics and working mathematicians, etc, are outright incorrect. I am reminded of George cantor and what he had to endure amongst 'the most learned'.

      (wikipedia)

      "The objections to his work were occasionally fierce: Poincaré referred to Cantor's ideas as a "grave disease" infecting the discipline of mathematics,[6] and Kronecker's public opposition and personal attacks included describing Cantor as a "scientific charlatan", a "renegade" and a "corrupter of youth."[7] Writing decades after Cantor's death, Wittgenstein lamented that mathematics is "ridden through and through with the pernicious idioms of set theory," which he dismissed as "utter nonsense" that is "laughable" and "wrong".[8] Cantor's recurring bouts of depression from 1884 to the end of his life were once blamed on the hostile attitude of many of his contemporaries,"

    21. Re:Machine Readable ? by David+Jao · · Score: 1

      How many formal proof languages have you seen? Most of them are designed for software verification, not formalized mathematics. They are optimized to make it easier for the author, not for the reader.

      Indeed, write-only code is a key aspect of perl which is shared by every formal proof language.

      Vdash will (probably) use Isar which is as easy to read for a mathematician as a standard proof.

      In order for this claim to be true to the extent that it would affect my assertion about advancing (or not advancing) the development of new mathematics, one would at a minimum need to be able to efficiently write existing proofs in the formal language (surely one cannot hope to accelerate the discovery of new proofs if even the existing literature cannot be efficiently handled). That means formal proofs for things like Fermat's Last Theorem, Poincare Conjecture, and so on, which I honestly don't ever expect to see in my lifetime.

    22. Re:Machine Readable ? by slawekk · · Score: 1

      In order for this claim to be true (...) one would at a minimum need to be able to efficiently write existing proofs in the formal language

      I don't quite follow your reasoning. In order to convince you that some proof languages are readable I would need to be able to write formal proofs efficiently? Ease of writing formal proofs is not much related to readability. As I mentioned, languages that are designed to make writing the proofs easier tend to be less readable. For some examples of machine verified proofs that I consider readable you can look at the Tiddly Formal Math site (disclaimer: I am the author of that site). As for what will be formalized in someone's lifetime it's a moving target. People used to say that the prime number theorem will not be formalized in their lifetimes and many were wrong. I am happy that the proofs being mentioned in this type of argument now are much more recent. I think formalizing large areas of mathematics will advance the development of new mathematics in about the same extent as development of modern foundations of mathematics at the end of XIX century. It was not obvious to see at that time as well why there was even a need, and how it would help.

    23. Re:Machine Readable ? by David+Jao · · Score: 1

      I don't quite follow your reasoning. In order to convince you that some proof languages are readable I would need to be able to write formal proofs efficiently? ... As I mentioned, languages that are designed to make writing the proofs easier tend to be less readable.

      Readability and writeability are separate and diametrically opposed issues. Writeability is necessary in order to speed up the development of new mathematics. Readability is necessary in order to improve the general public's understanding of and accessibility to the project. We apparently both agree that readability and writeability are conflicting goals. I am of the opinion that machine readable proofs are currently inadequate on both counts, i.e. machine readable proofs are not useful for developing new math, and they are also not useful for teaching mathematics to the general public. You on the other hand seem to be convinced that machine readable proofs are adequate on both counts, despite the conflicting nature of these goals.

      I hope that the above accurately summarizes our positions. If not, feel free to correct any mistakes that I have made.

    24. Re:Machine Readable ? by slawekk · · Score: 1

      Readability and writeability are separate and diametrically opposed issues. (...) We apparently both agree that readability and writeability are conflicting goals.

      Not exactly. My opinion is that readability and writeability are orthogonal in the design of a formal proof language. For most formal proof languages the design effort was invested in writeability because those languages were intended to be used for formal verification of software. However, mathematicians are not only interested in the fact that the assertion of a theorem is true, but also want to know why it is true, i.e. they want to be able to read the proofs. There is a line of formal proof languages whose design goal is readability (Mizar, Isar and the declarative proof language for COQ ). After getting used to, proofs in those languages are as readable as standard (informal) proofs.

      machine readable proofs are not useful for developing new math, and they are also not useful for teaching mathematics to the general public

      Well, if you phrase it this way I agree. Writing formal proofs will always be more difficult than writing the standard ones. This is because they contain much more information. It is not useful for a mathematician to write his/her proofs in a formal proof language before publication. In most cases it is not even practically possible because there is not enough background in formalized form. So, if you are a mathematician, formalized mathematics will not be of much use. It will not advance your career. It may inhibit it as it is a bit addictive and may consume the time you should spend writing publications and grant proposals. It is also not useful for educating general public. It typically requires some background in the foundations, like set theory. General public doesn't know set theory. General public doesn't know how to add fractions. So what is formalized mathematics good for? I personally do it for fun and as expression of creativity. I think it may be useful for getting more information about existing mathematics. For example, take the role of the axiom of choice in the construction of Lebesque measure. Since in ZF you can not prove that real numbers are not a countable union of countable sets, you can not construct the Lebesque measure (or any nontrivial measure on real numbers that assigns zero to all singletons) without using the axiom of choice somewhere. Where exactly is it used? What can you get without it? It would be very easy to find out if we had a formalized construction. Another use of formalized mathematics could be learning mathematics not by the "general public" but by the students of mathematics. We may disagree on that since you don't believe that formal proofs can be made readable. But I think they can, and if they are structured well, as Isar allows, the machine can display the desired level of detail, zoom in if some step is not clear and zoom out if some part is (seems) obvious. This use is more about knowledge representation than correctness of proofs.

    25. Re:Machine Readable ? by Anonymous Coward · · Score: 0

      Writing formal proofs will always be more difficult than writing the standard ones. This is because they contain much more information. It is not useful for a mathematician to write his/her proofs in a formal proof language before publication. In most cases it is not even practically possible because there is not enough background in formalized form.

      You are describing the situation as it stands today. However, the availability of powerful interactive proof environments combined with a "standard library" of formalized results could radically alter the character of mathematical research.

      First of all, even if we were to forgo complete verification, proof assistants can help in managing more complicated theories by keeping track of hypotheses, proof obligations, etc.

      Additionally, mathematicians tend to neglect known results and techniques outside of their own specialty, since they don't clearly understand the underlying assumptions. Having the formal statements of such results available would obviate this problem and encourage reuse of mathematical theorems.

      As for the addictive character of formalized mathematics: that's a feature, not a bug! As of today, many mathematicians find that their productivity is constrained by the need to get bogged down in tedious details - this is especially true of older researchers, who have long become acquainted with the underlying ideas and concepts in their field.

  6. What? by moniker127 · · Score: 1

    They did what with the who in the wikihow?

  7. Yay! Truth Mines! by seanellis · · Score: 2, Informative

    What? You haven't read Diaspora by Greg Egan? Shame on you!

    1. Re:Yay! Truth Mines! by treeves · · Score: 1

      No, but I once watched an episode of BJ and the Bear, with Greg Evigan. Does that count?

      --
      ...the future crusty old bastards are already drinking the Kool-Aid.
    2. Re:Yay! Truth Mines! by masterzora · · Score: 1

      Well-played, sir.

      --
      Remember, open source is free as in speech, not free as in bear.
  8. Who will prove the prover? by Rayban · · Score: 1

    Does this mean that Isabelle needs a formal proof to prove it works?

    --
    æeee!
    1. Re:Who will prove the prover? by Frans+Faase · · Score: 1

      This is indeed what one would expect. For that reason I find matemath far more interesting. Isabelle already has been use for some time. According to the wikipedia entry: "It is an LCF-style theorem prover (written in Standard ML), so it is based on a small logical core guaranteeing logical correctness."

  9. depends on kind of math. by porky_pig_jr · · Score: 1

    there are some areas like formal logic and staff which is heavily set-theoretical (like point-set topology) where automated provers are already available. you probably can add most of the algebra as well. OTOH, things like analysis (real, complex, functional) is much harder to formalize, many proofs end up with "now take epsilon to 0", or "take n to infinity", you have to deal with countable vs uncountable infinities. I'm not saying it's impossible to formalize, only that that's much harder.

  10. Use for the rest of us by philspear · · Score: 1

    That sounds great, but when will there be a computer which can solve my real-life math problems which mostly revolve around when will I pass Bob if Bob is driving at a speed in miles per hour from a place to a place at a time and I start driving toward the first place from the second place at a speed in kilometers per hour at a time? My current method of polling 4th graders isn't working very well.

    1. Re:Use for the rest of us by atraintocry · · Score: 1

      a computer which can solve my real-life math problems which mostly revolve around when will I pass Bob if Bob is driving at a speed in miles per hour from a place to a place at a time and I start driving toward the first place from the second place at a speed in kilometers per hour at a time

      The math part you could do on a calculator...but what you really have seems to be a language problem. :)

  11. machine-readable format by buchner.johannes · · Score: 1

    I played with the idea about making such a project a year ago, with dependencies between the lemma/theorems etc. in machine-readable format, but had no clue how to represent the understanding and terms of math in a consistent way. I'm interested in how they do that here...

    --
    NB: The message above might reflect my opinion right now, but not necessarily tomorrow or next year.
  12. Does this mean I can use Isabelle.. by QuantumG · · Score: 1

    without EMACS? Now that is progress.

    --
    How we know is more important than what we know.
  13. Infinite by buchner.johannes · · Score: 1

    Can't you derive an infinite or at least an enormous number of true theorems from the existing ones? Do they and if, how do they remove "duplicates"/"extras" that are not theorems, much more corollaries?
    As pure mathematicians they might be interesting in doing so :-/ no?

    --
    NB: The message above might reflect my opinion right now, but not necessarily tomorrow or next year.
    1. Re:Infinite by david_thornley · · Score: 1

      There are an infinite number of theorems. For a trivial example, each entry in the multiplication table can be expressed as a theorem. You could regard multiplication, as you learned in grade school, to be a constructive proof of a theorem (given proper axioms, such as the table up to 9x9). The question is not so much how to remove duplicates, as how to remove the less interesting ones so you can find something useful in the batch.

      As I understand it (I have, of course, not RTFA), these proofs will be submitted by actual humans, and therefore will pass the filtering process of being interesting to at least one mathematician (defining a mathematician as somebody who can present a theorem and proof that'll be accepted by the computer). Of course, if individual submitted theorems start being counted as publication credits, they may need to filter for interestingness rather than correctness.

      --
      "When you have eliminated the unacceptable, whatever is left, however improbable, must be the truthiness" - Holmes
  14. obtuse/esoteric dialogue by j1m+5n0w · · Score: 1

    My experience with math professors is that most of them are able to present clear explanations of the subjects they're teaching without referring extensively to topics that are more advanced than the topics at hand.

    On wikipedia, however, "obtuse/esoteric dialogue" seems to be the norm, and I have very rarely been able to understand a math article about a topic that I didn't already understand. I hope that this trend will eventually correct itself by better editing.

    1. Re:obtuse/esoteric dialogue by TheEmptySet · · Score: 1
      While I'm here defending the profession...

      Wikipedia is great for maths. I use it a lot. When I look something up I don't necessarily understand all the terms used to explain it, so I click on some of the links to explain those terms,... etc.

  15. Zombie David Hilbert... by weston · · Score: 1

    ... laughs at your difficulties.

    (but is afraid of zombie Kurt Gödel.)

  16. MIT is late to the party by jipn4 · · Score: 1

    Formally verified mathematics has been around for decades; it's just hard. Putting it into a wiki won't make it any easier.

    1. Re:MIT is late to the party by azgard · · Score: 1

      I partly disagree. For example, Euler had no real understanding of real numbers and issues around them - for him, almost every function was continuous. Around 1900, you could also say that formalized mathematics (using logical quantifiers everywhere, starting from set theory) is very difficult when compared to more intuitive classical methods. Now we teach this way to students.

      Formal mathematics on computer is the next step, just like logical formalization was, and all mathematicians will have to adapt to it. They will manage - they're smart. I think that every serious mathematical course should teach how to use formal proof systems, and what the basics of terminology and working of it are.

      In the end, formalization of proof is not so much harder. For example, IIRC, in Mizar system average proof length is about 4 times longer than the equivalent proof readable by humans. This is an excellent ratio for a computer understanding something, and probably with further engineering could be even reduced.

      The important step is to put the formal proving systems into mainstream, and I hope this wiki will help with this. Especially if it will be open for any mathematician, and there will be good tutorials on principles.

    2. Re:MIT is late to the party by jipn4 · · Score: 1

      I partly disagree.

      I'm not sure what you're disagreeing with. Most of what you write has nothing to do with my point.

      The important step is to put the formal proving systems into mainstream,

      Yes, and there have been lots of systems trying to do that. This wiki seems no easier to use than many of the other attempts at doing this; so what's MIT's contribution?

    3. Re:MIT is late to the party by azgard · · Score: 1

      I disagreed with the statement that formal computer mathematics is hard - I believe it's a matter of user interface, teaching it mathematicians and good tutorials. I believe most of this "hard" is just an illusion from people who don't know it (myself included). I already elaborated why I think so.

      The important thing there is social, I think. The system needs to be open for all mathematicians (or general public), and there should be good tutorials for it.

    4. Re:MIT is late to the party by jipn4 · · Score: 1

      It's hard because the user interfaces have been bad. The existing user interfaces actually do a lot of bookkeeping and give the users interactive feedback. A Wiki does less of that, not more, so it's not going to help.

  17. Axiom of choice by JuanCarlosII · · Score: 1

    Will there be some preferences where I can decide if I assume the axiom of choice or not? The content must surely vary accordingly? Seriously though, this does seem like an interesting project but a wiki is hardly the correct format if the proofs are all going to be "machine readable" and more importantly "machine verifiable". I can't help but foresee several years of work going into converting the very simplest of theorems into "machine readable" format long before anything interesting gets included. Must confess I can't help thinking that AI just isn't up to it, and there isn't enough Human Intelligence willing or able to commit the millions of hours required to actually make something like this work.

  18. Liberatory Mathematics by rumblin'rabbit · · Score: 1

    One of the criticisms of mathematics is that mathematicians claim truth and rigour, yet in practise their proofs are often quite sloppy. In other words, most proofs are convincing rather than rigorous. Thus some have suggested that mathematics is made up of opinions rather than logically true assertions.

    Some "scholars" from the humanities have used this to suggest we develop a postmodern, liberatory mathematics, freed from the tyranny of logical proof, and thus from the oppressive hegemony of the modern militaristic patriarchy.

    This project might help to stem such blather. Although, as they say, you can't reason someone out of a position if they never reasoned themselves into it in the first place.

    1. Re:Liberatory Mathematics by Nefarious+Wheel · · Score: 1

      One of the criticisms of mathematics is that mathematicians claim truth and rigour, yet in practise their proofs are often quite sloppy. In other words, most proofs are convincing rather than rigorous.

      Hear hear! How many proofs have you seen that are some variation of "Given the total body of known mathematical thought; the proof follows by inspection."? QED.

      --
      Do not mock my vision of impractical footwear
    2. Re:Liberatory Mathematics by eggstasy · · Score: 1

      Normal math already uses unproven conjectures and hypotheses.
      There are things which seem fairly intuitive even to laymen but are very hard to prove.
      I am reminded of a theorem I learned about in college, that went unproven for ages: i think it was something like "given a closed loop, a point can only be either inside or outside it"
      http://en.wikipedia.org/wiki/Conjecture
      http://en.wikipedia.org/wiki/Riemann_hypothesis

    3. Re:Liberatory Mathematics by aldo.gs · · Score: 1

      Well, they can use conjectures, but the "result" is often preceded by "If P is true, then the result is true, however...". The thing is that sometimes the "result" appears to be valid in many situations thus making the conjecture on which it depends appear more likely to be true (I mean that it can be proven using the other 'standard' axioms, rather than taking the conjecture as an axiom in general).

      And perhaps you mean the Jordan curve Theorem? Yeah, that bastard is really intuitive but the proof is kinda hard. May I suggest -if you are interested- reading Guillemin's Differential Topology, there is a "proof" of a general version of the theorem (more like a series of exercises to prove the theorem). Very accessible book, if one is willing to believe many things without actually checking their proofs thoroughly.

    4. Re:Liberatory Mathematics by azgard · · Score: 1

      Efforts like this one already exists.

      For example, there is Mizar system, which is a proof checker with about 46000 correct theorems in his database. So large parts of basic mathematics have already been formally verified.

      What is new in this project is the fact that it's a wiki, so anyone can add new assertions. That's improvement, and I believe that this openness will encourage all mathematicians to converge to some site like this in the future.

      This will ultimately benefit mathematics, because it will make research much more efficient. For example, it would be very nice to know that the theorem you need for your application has already been proven and that there is a nice theory around it. Formalization of all mathematics in computers is a first step in that direction.

    5. Re:Liberatory Mathematics by Secret+Rabbit · · Score: 1

      """
      yet in practise their proofs are often quite sloppy
      """

      And the people who say this are the ones that don't understand that each and every word has profound meaning. As in, in some books, it's not uncommon for someone who's learning, to spend an hour or more on one page unwinding it. Also, though some wording still may /appear/ sloppy, even after that, in the end, that "sloppy" wording is nothing more than a few lines of rigorous Math. You can't write *everything* out. Especially in a journal. It would produce prohibitive amounts of pages.

      From my Complex Analysis book (Marsden and Hoffman, 3rd ed.) an example would probably be Thm 1.5.4 (I believe it's that one - it's been a while and the papers with these "corrections" that I wrote and inserted at those points fell out and disappeared). In the proof, there is a step that is "hand waved" over. At the time, I asked the Prof, and all he said is, (paraphrase) "It's obvious. I don't know what to explain." Took me a bit, but the hand wave ended up being about 5 lines long and it probably should have been obvious. Here's to hitting dead brain cells (and/or being burned out).

      At any rate, not so much sloppy. More along the lines that the people who know that they are talking about will just "see" those lines where they aught to be. And again, without that, the length of the papers in journals would be too wordy and long to be practical.

    6. Re:Liberatory Mathematics by rumblin'rabbit · · Score: 1

      I agree that mathematics would be tedious if every proof was machine-verifiably rigorous. I'm not really criticizing the practise, since I do the same myself.

      In text books the mathematics is usually high quality, even when some steps are glossed over. In journal papers, however, things can get much looser. Indeed, my guess is that there are quite a few inadequate or incorrect proofs.

    7. Re:Liberatory Mathematics by n00854180t · · Score: 1

      Does the proof in Guillemin's treat the case of dimensions greater than 2? It seems like most places that deal with it do so by putting things in terms of the plane that the loop and the point lie on. If you had a closed loop in 2d in a 3d space, and the point wasn't coplanar with the loop, it could potentially be both "inside" and "outside" the loop, depending on the position it was viewed from (though, I have a feeling that this really doesn't matter, since in the 3d case you're either going to have it be a 3d loop of some sort, or require the point to be coplanar). I'm not a mathematician, so I'm sure I'm just mucking everything up here :)

    8. Re:Liberatory Mathematics by Secret+Rabbit · · Score: 1

      But, that's what peer review and paper retraction is for. I won't name names, but I know for a fact that papers are retracted when an error is found. Also, since everyone builds on everyone else's work, the errors have a tendency to be found (it's hard to hide inconsistencies when they become obvious). It might not happen instantly, but it will happen eventually. Hell, even axiomatic Mathematics itself is a *very* young idea.

    9. Re:Liberatory Mathematics by aldo.gs · · Score: 1

      Yes, the proof is for the n-dimensional case. The drawings are still of a loop in (on?) the plane, though :P. But yeah, your idea of 3d loop is what the author uses (in the book it's called a 'hypersurface' and it shows that it's actually the boundary of a compact manifold, and there are two connected components: 'inside' and 'outside' the hypersurface).

    10. Re:Liberatory Mathematics by n00854180t · · Score: 1

      Awesome, thanks :) Pretty much as I figured (I was putting it into layman's terms for my own sake, since I would, without a doubt, botch the maths terminology). OT/for curiosity's sake: Is the typical maths terminology "in a/the plane", as you have it with my usage in parentheses? I always think of things as lying "on" a plane (i.e., a point on a plane in a 3-space) simply because that's the case I'm used to dealing with (I'm a game programmer) and it makes sense from the point of view of the numbers one sees when debugging (that is, if the plane is defined by a point and a normal, then a point lying "on" the plane to me would end up having the same values for x/y (in the case where the plane is defined by a point and a normal in either x or y)).

    11. Re:Liberatory Mathematics by rumblin'rabbit · · Score: 1

      For the more popular streams of mathematical research I agree, and this is what keeps mathematics on its feet.

      But there are many branches of mathematics of which there are only a few people in the world doing work, and many papers have little impact and thus are not carefully scrutinized after publication. And occasionally some proofs are so tedious or complex that perhaps no one outside of the author really understands them.

      Furthermore some journals, departmental technical reports, and most conference papers are only loosely peer reviewed, and some not at all. I do peer review myself, and thus have a skeptical attitude of the process to right all wrongs.

    12. Re:Liberatory Mathematics by aldo.gs · · Score: 1

      It depends what you mean. In most cases the use is "in the plane" because the point is actually a part of the plane (an element in the set that we call 'plane', to be precise) instead of merely being on it. I hope this explains the difference.

      Completely offtopic now :P :
      Oh, cool, what kind of games do you program? I once coded a game of hangman in C, and I'm trying to learn Java (mostly because I don't have windows but I want to share the programs I create), is there a book you'd recommend (especifically I'm trying to understand events: listeners and all that)?

    13. Re:Liberatory Mathematics by n00854180t · · Score: 1

      Ahah, makes sense. I merely wasn't thinking of it as a set.

      The company I work for is a small independent house, we've been doing mainly contract work. The biggest "game" project we've done is a simulation for museums (first person dinosaur game) called BeTheDinosaur.

      Personally, I would steer clear of Java and look at something like SDL in order to get cross platform support (assuming you're doing games...Java is fine for some things, but at least IMO, games aren't it). As far as event/listener systems go, I don't know of any books myself, but I'm sure you can find some on Amazon in either one of the "Event-Driven Programming" or "Design Patterns" type books. A co-worker also suggested checking out C#'s implementation for ideas (since you don't use Windows, Mono would be your best bet there).

  19. vapourware by QuantumG · · Score: 1

    I sounds like a great idea. So, umm, do it.

    --
    How we know is more important than what we know.
  20. 8 entries for 'mathematics' by davejenkins · · Score: 3, Informative
    If you don't like this one, help yourself to the others (from wikindex.com, in order of activity):
    • http://www.exampleproblems.com/ ExampleProblems Wiki Graduate level mathematics example problems with solutions.
    • http://maple.wikia.com/ Maple This page is all about the The Maple Wiki.
    • http://diffgeom.wiki-site.com/ Diffgeom This wiki is about differential geometry and related facets of ...
    • http://www.mathcasts.org/ Mathcasts Mathcasts are screencasts (screen movies) which are created and shared to improve the learning and teaching of mathematics. Mathcasts were originally called math movies and then Whiteboard Movies but when the term screencasts became popular mathcasts seemed like a great name for them.
    • http://math.wikia.com/ Mathematics Wiki Mathematics is a Wikia for the collection of math-related news, ...
    • http://algorithm.wikia.com/ Algorithm In mathematics and computing, an algorithm is a procedure (a finite set of well-defined instructions) for accomplishing some task which, given an initial state, will terminate in a defined end-state. The computational complexity and efficient implementation... Algorithm The Algorithm Wikia is a wiki for gathering the latest
    • http://gametheory.wikia.com/ GameTheory The Game Theory Wikia is a wiki about applied mathematics ...
    • http://matheaufgaben.wikia.com/ Matheaufgaben Matheaufgaben Mathematics is a Wikia for the collection of math-related news, ...
    1. Re:8 entries for 'mathematics' by Anonymous Coward · · Score: 0

      How is this project significatly different from the metamath project?

      metamath.org already has over 8,000 theorems (all with machanically checked proofs) covering a significant chunk of modern mathematics.

    2. Re:8 entries for 'mathematics' by Anonymous Coward · · Score: 0

      metamath.org is a similar project, already having over 8000 proven theorems covering a good part of current mathemtatics.

  21. I've heard this one before by Kennego · · Score: 1

    Oh it sounds like a great idea now, technology able to reveal previously undiscovered connections.

    But then they'll finish it, call it the Intersect, and it'll accidentally get downloaded into the brain of a computer repair tech. Then what?

  22. If then, so: by mencomenco · · Score: 1

    "thus advancing some fields with no further work being necessary."

    And presumably with no need for further mathematicians.

    The Chinese will be furious.

  23. Been doing this since 2001, someone plz vote me up by adougher9 · · Score: 0

    frdcsa.org frd stands for Formalized Research Database. been doing this since 2001. there is also FDL (formal digital library)

  24. Re:Been doing this since 2001, someone plz vote me by adougher9 · · Score: 0
  25. Machine proofs are a farce by Secret+Rabbit · · Score: 0, Troll

    This is totally nuts. Machines CAN NEVER BE AS GOOD AS THE ONES THAT PROGRAM THEM. For that to be so, it'll require creativity, etc. Computers, at least now, have no such capacity. After all, how are new proof techniques supposed to be checked when they are an unknown quantity? This is total BS.

    If one wants an example of such things gone awry, you need to look no further than James Anderson's Transreals. There exists proofs that they are inconsistent at the axiomatic level, but James just states that he has a machine proof that states they are consistent and ignores the proofs completely. In fact, his response to the criticism has been the typical political speak of not actually addressing anything.

    Given the above, you'll have to excuse me while the Mathematical community at large and myself completely ignore and shun this.

    1. Re:Machine proofs are a farce by QuantumG · · Score: 1

      I think I speak for everyone when I say: you're an idiot.

      At least you've managed to find Slashdot, well done.

      --
      How we know is more important than what we know.
    2. Re:Machine proofs are a farce by Secret+Rabbit · · Score: 1

      And for not saying why, that makes you what again?

    3. Re:Machine proofs are a farce by QuantumG · · Score: 2, Funny

      A smug bastard who would rather point and laugh at you than educate?

      --
      How we know is more important than what we know.
    4. Re:Machine proofs are a farce by Rakishi · · Score: 1

      Machines CAN NEVER BE AS GOOD AS THE ONES THAT PROGRAM THEM.

      Sure they can and you don't even really need to "program" much into them, just look at biology and evolution.

    5. Re:Machine proofs are a farce by Alpha830RulZ · · Score: 1

      Machines CAN NEVER BE AS GOOD AS THE ONES THAT PROGRAM THEM.

      My mother has been saying this about me for years.

      --
      I was taught to respect my elders. The trouble is, it's getting harder and harder to find some.
    6. Re:Machine proofs are a farce by Secret+Rabbit · · Score: 1

      Rather someone who doesn't know the limitations of a computer (they do have limitations you know) and doesn't have anything of substance to say.

      I'll never understand why some people think that because its done on a computer, it makes it better. There are always bugs and because of that, it's no more infallible than humans. It'll just make the mistakes faster and *much* harder to detect.

      Overconfidence never leads to good places.

    7. Re:Machine proofs are a farce by Secret+Rabbit · · Score: 1

      Wholly out of context Batman!

    8. Re:Machine proofs are a farce by NotBorg · · Score: 1

      Overconfidence never leads to good places.

      How sure are you about this?

      --
      I want this account deleted.
    9. Re:Machine proofs are a farce by Rakishi · · Score: 1

      You're just not very imaginative, living things are really no different from machines. So unless you believe everything was made by god it's already quite evident that relatively simple machines (cells) can without prior design create intelligent beings. In other words it not that hard to make machines that are better than their creators assuming you have sufficiently good technology.

    10. Re:Machine proofs are a farce by Rakishi · · Score: 1

      Rather someone who doesn't know the limitations of a computer (they do have limitations you know) and doesn't have anything of substance to say.

      You're the only one here who seems to not understand the limitations of either computer or humans.

      Overconfidence never leads to good places.

      Quite true, human confidence does prevent automation of many areas due to a false belief that humans are better.

      I'll never understand why some people think that because its done on a computer, it makes it better. There are always bugs and because of that, it's no more infallible than humans. It'll just make the mistakes faster and *much* harder to detect.

      Many computer programs are a lot less error prone than humans as even something as simple as simple mathematics would show (just give them enough numbers that are large enough). There is nothing that says computer bugs have to appear just as often as human fuckups. Computer code will pretty run the same every time which means it has to only be debugged at one point while humans can make a mistake even if they did the exact same thing correctly 10000 times.

    11. Re:Machine proofs are a farce by Secret+Rabbit · · Score: 1

      You're cherry picking your data i.e. simple arithmatic is _not_ what we're talking about. What we /are/ talking about is something that is exceedingly complicated and dynamic that requires creativity. And that is exactly the type of thing that computers are bad at. If you understood something about higher Mathematics you wouldn't be making such asinine statements.

      Btw, I have both a Programming Diploma AND a Degree in Mathematics. I've also did research in a Physics department as a student which involved numerical analysis and have talked to several people regarding automated proof checkers/creators. The theory behind these things, never mind there practical implementations are *far* to immature to be practical. Not to mention that it is questionable if they are even feasible to create on a fundamental level.

    12. Re:Machine proofs are a farce by Secret+Rabbit · · Score: 1

      How is it that you've missed my point even when I stated it? Are you trying to be obtuse for a purpose? Because, my reply indicated that I knew what you were talking about, but that YOU took what my obvious point what out of context. Would you care to actually contribute to the conversation? Or are you just going to continue to 'not get it'?

    13. Re:Machine proofs are a farce by Secret+Rabbit · · Score: 1

      I could add on, "in the end." Would that satisfy your nit-picky-ness? Because, I've *never* heard of overconfident people not getting screwed by there overconfidence at some point (usually sooner rather than later).

      Now, a question: What does this have to do with the topic at hand, or the point that I was making? How would this "sloppy" wording effect what I'm saying in any significant way?

    14. Re:Machine proofs are a farce by S7urm · · Score: 1

      Regardless of this person's vanity whoring, he's right. Any Input based medium can only contain/compute computations that are at one point input by a "user". The only benefit a computer has is parallel processing and the ability to more QUICKLY render sumations. Thus a computer is and will always be at a level where it can not create, only calculate. I'd say you define intelligence or creativity differently than most.

      --
      "This is the value of a summer spent and a winter earned"
    15. Re:Machine proofs are a farce by Secret+Rabbit · · Score: 1

      And that quicker can quickly become not quicker when the basic rules are too basic to make it feasible to enter the theorem/proof in a timely manner. Not to mention that the input will suffer from human error on entry. So, the proof might be correct, but the come out as incorrect if (really when) the theorem is incorrectly entered. And of course, vis versa. And lets be honest. When we have fairly high error rates on simple data entry (e.g. numbers), how much higher is that going to be when we have something as complicated as this?

      I also wouldn't say that I define creativity different than most. More along the lines that I have knowledge about a topic that most don't understand. So, most will not appreciate what is meant by creativity in Mathematics when most people don't understand just how creative one has to be to do higher Mathematics. This is probably so because the vast majority of people have only heard of Analysis (IF they've heard of it) and have never seen what it really is (similarly for other fields in higher Maths).

    16. Re:Machine proofs are a farce by NotBorg · · Score: 1

      I am confident you do not have a sense of humor.

      The point is that you come off as very confident (overly so maybe?) that you are absolutely correct. Its funny because you are also bent on the notion that overconfidence will screw you.

      Type LOL and let it slide not everyone gets infinite recursion the first time around.

      --
      I want this account deleted.
  26. Still an open field for flamewars by Anonymous Coward · · Score: 0

    Including only formally verifiable theorems (and preferably the wiki will have a built-in mechanism to automatically check all submitted theorems with no human intervention) will make impossible vandalism or honest mistakes in the form of errors.

    But, this is far from having a neutral, impartial wiki. A theorem prover can prove an infinite number of true theorems, but almost all of them will be useless. It still takes human involvement to judge a theorem by its importance, whether in the form of inherent importance to mathematics, some empirical usefulness, relevance to another theorem (as lemmas are), some distinguishing or unique feature not covered in a previous case, or simply a particular example mathematical beauty.

    This kind of selection is inherently subjective - if machines could do it, we wouldn't need human mathematicians. But this also means there will surely be debates about what kind of content is important enough to include.

    Plus, of course, all your theorems will depend on your set of axioms and rules of inference, from accepting/rejecting the Axiom of Choice, to proponents of non-classical logic.

    Choice of wording, structure, organization, categorization, etc. is also up in the air, and there will definitely not have a single opinion about the right way to do any of that.

    Machines may prove the theorems, but it'll be humans who ultimately write the wiki. Sure, that wiki might be more neutral, impartial, and formal than Wikipedia. But it certainly won't completely lack ambiguity and subjectiveness that are natural to humans, which is both a strength and a weakness.

  27. But is it reliable? by yafujifide · · Score: 1

    I won't believe this site works as claimed until I see it on vdash.org.

  28. Automatically generating all truth by Anonymous Coward · · Score: 0

    If this worked couldn't you just submit all possible strings of text increasing in length to proof checker until you proved anything that was likely to be useful.

  29. Everything true? by cpscotti · · Score: 1

    Wouldn't this project be another "armageddon" machine (LHC..)? What if someone finds a bug in it 25 years from now? A bug that generates a contradiction? It would prove EVERYTHING to be TRUE (and FALSE). OHH GOD! STOP IT!

  30. Metamath by Anonymous Coward · · Score: 0

    Wouldn't it be better to get something like an ajax version of http://metamath.org/ up?

  31. Machine Readable Language by valdis · · Score: 1

    Just for the record, if you're dealing with "machine readable language", what you want is the Turing Halting Problem, which is essentially the same mathematical derivation Godel used for theorems, but applied to algorithms.

    1. Re:Machine Readable Language by Free+the+Cowards · · Score: 1

      You're only dealing with it if you're trying to decide if it halts (or if it's true, i.e. Godel's version).

      This wiki will not do that. It does not claim to do that.

      I don't understand why people cannot grasp this. All it does is automatically check a human-given proof that accompanies a human-given theorem. This is not revolutionary or even very hard. Why people feel the need to bandy about claims of mathematical impossibility is utterly beyond me. It has nothing to do with Godel's theorem.

      --
      If you mod me Overrated, you are admitting that you have no penis.
    2. Re:Machine Readable Language by caramelcarrot · · Score: 1

      There seems to be a large number of armchair philosophers in this thread and I salute you for trying to fix misconceptions!

  32. Tell me when it's on iTunes by kjllmn · · Score: 1

    I'd like to see the theorems turned into code turned into music. Or, rather, Id like to hear the theorems turned into code turned into music.

  33. Skip the stories by kylemonger · · Score: 1

    It is a much better book if you skip the Achilles, Tortoise, etc. stories. Read them only if you can't understand the math without the analogies the stories provide. GEB was a huge help in understanding what Godel was talking about for me.

    What I was left wondering after finishing the book is whether there are any interesting truths that lie outside those provable by Peano arithmetic about Peano arithmetic.

  34. Nicolas Bourbaki by slashmais · · Score: 1

    Maybe they can pick up some caveats from the Bourbaki fraternity.
    http://en.wikipedia.org/wiki/Bourbaki
    An interesting article (well worth reading) is here: http://planetmath.org/encyclopedia/NicolasBourbaki.html

    --
    time time everywhere and not a second to spare
  35. How do we know that Isabelle is correct? by rrohbeck · · Score: 1

    Has anybody proven that?

    1. Re:How do we know that Isabelle is correct? by Secret+Rabbit · · Score: 1

      There's the rub though, eh. The bugs that will *always* be in there... What will they do to the conclusions?

      Blindly trusting machines to do this (or close to it), when in the end it's Math that is depended on to see whether buildings will stand during an earthquake, etc, is irresponsible.

    2. Re:How do we know that Isabelle is correct? by Jamie+Lokier · · Score: 1

      Do you think humans are more reliable? What makes you think that? And what makes you think the same principles that allow you to trust humans more cannot be replicated in machine form?

    3. Re:How do we know that Isabelle is correct? by Secret+Rabbit · · Score: 1

      Humans can admit mistakes, computers are only capable of following rules written by humans. So, when an error is found that results in an inconsistency, humans will follow the chain to find the error. Computers on the other hand aren't capable of doing this. It's called lack of creativity. Computers just don't have it.

      Just because something is faster, does _not_ mean it's better. It just means that WHEN an error is produced, it'll do it a hell of a lot quicker. But, who will notice if no-one is checking the checker?

      Also, this isn't some 2 + 2 nonsense. This is higher Mathematics. So, when someone write a paper with something along the lines of:

      Taking (23), we proceed by partial fractions which results in: ...

      How exactly is that supposed to be easily translate/automated?

      In all honesty, the only reason why I can think of that people so violently defend this flawed notion is a utterly complete misunderstanding of what Mathematics really is and how it is done. I mean, come on. Most of us work with/fix computers daily. Can we at least be honest and admit that trusting a program to do such a complicated creative thing is a bad idea? I mean, just look at the quality of software out there...

    4. Re:How do we know that Isabelle is correct? by Jamie+Lokier · · Score: 1

      Humans can admit mistakes, computers are only capable of following rules written by humans. So, when an error is found that results in an inconsistency, humans will follow the chain to find the error. Computers on the other hand aren't capable of doing this. It's called lack of creativity. Computers just don't have it.

      I think you have a narrow view of how computers are able to function. Not all computers work by following instructions.

      Take an analogue neural net, as just one of many examples: it can function in ways that the designers do not understand, and it doesn't have instructions at all. GAs too. The source of creativity can be information from the environment which is impossible to trace but manifests through the processes of the machine, and anomalies baked into its physical structure which you can never reproduce exactly.

      Also, what rules out programming an instruction-based computer to apply peer review with other computers and be programmed to admit mistakes and follow chains to find errors?

      I agree with your premise, btw, but I'm asking how do you justify that premise beyond saying "they lack creativity and self checking", as at least some forms of both those things can be realistically expected to arrive in computers at some point.

      Taking (23), we proceed by partial fractions which results in: ...

      How exactly is that supposed to be easily translate/automated?

      That's quite possibly a natural language problem, not a mathematics problem. Nobody said it was easy.

      But, who will notice if no-one is checking the checker?

      [...] I mean, come on. Most of us work with/fix computers daily. Can we at least be honest and admit that trusting a program to do such a complicated creative thing is a bad idea? I mean, just look at the quality of software out there...

      Oh, I agree with you completely on that :-)

      I'm just wondering why you trust humans?

      In my experience, most humans are quite poor at mathematics and reasoning. They are also quite poor at admitting mistakes, or even understanding their mistakes sometimes.

      I would trust really good mathemticians to do mathematics, but they are a tiny minority. Conceivably if there were 6 billion different computer mathematics programs out there (there aren't), then I might trust a small number of those too, once they have demonstrated their effectiveness and reliability as far superior to others.

    5. Re:How do we know that Isabelle is correct? by Nicolay77 · · Score: 1

      Well, if you are a mathematician you understand this: Any single software system that doesn't have any bug proves that your assertion "all software systems have bugs" is false.

      Just because lots of companies write sloppy code doesn't mean that ALL code ever written is sloppy and buggy.

      To me you don't know how computers work. You act like all the software has to work like Windows or Unix, and be programmed in C or C++.

      Ohh that's all that they sell in retail now. Sorry, I know why you have your preconceptions.

      A bug free computer system is possible, just think about banking systems that have been running for years. Or some of the stuff written by the military that controls planes or other realtime systems. Or the TeX system developed by Knuth.

      We can prove the correctness of software just the same as any mathematician proves a theorem. And we can reuse the stuff easier than a mathematician can.

      The problem is, bug free software is about 10 to 100 times more expensive to write. And no one will pay USD$25000 for a copy of Windows.

      Now, we can take an order of magnitude more time to write this system and make it bug free than the time we can spend writing its equivalent "ship fast because we have to sell" commercial system.

      It will take a huge amount of time. But I'm sure it can be done. After all, we the humanity have written bug free mathematical proofs, and lots of those proofs are harder than the system programming you are irrationally afraid of.

      --
      We are Turing O-Machines. The Oracle is out there.
  36. "true theorems" by RevWaldo · · Score: 1

    Aren't all theorems supposed to be true? Isn't this like saying "ATM machine"?

  37. Godel's second incompleteness theorem explained by Anonymous Coward · · Score: 0

    Kurt GÃdel (b. 1906, d.1978) made significant contributions to mathematical logic, set theory, and philosophy, but he is most widely recognized for his incompleteness theorems, arguably the most profound results in logic since Aristotle. He proved, in 1931, that no formal mathematical system can prove all mathematical truths. Put more crudely, he proved that truth is a stronger criterion than proof. To get a taste for this claim, consider this light-hearted extract from the essay, "Godel's second incompleteness theorem explained in words of one syllable", by George Boolos (1994):

    Quote:
    First of all, when I say "proved," what I will mean is "proved with the aid of the whole of math." Now then: two plus two is four, as you well know. And, of course, it can be proved that two plus two is four (proved, that is, with the aid of the whole of math, as I said, though in the case of two plus two, of course we do not need the whole of math to prove that it is four). And, as may not be quite so clear, it can be proved that it can be proved that two plus two is four, as well. And it can be proved that it can be proved that it can be proved that two plus two is four. And so on. In fact, if a claim can be proved, then it can be proved that the claim can be proved. And that too can be proved.

    Now: two plus two is not five. And it can be proved that two plus two is not five. And it can be proved that it can be proved that two plus two is not five, and so on.

    Thus: it can be proved that two plus two is not five. Can it be proved as well that two plus two is five? It would be a real blow to math, to say the least, if it could. If it could be proved that two plus two is five, then it could be proved that five is not five, and then there would be no claim that could not be proved, and math would be a lot of bunk.

    So, we now want to ask, can it be proved that it can't be proved that two plus two is five? Here's the shock: no, it can't. Or to hedge a bit: if it can be proved that it can't be proved that two plus two is five, then it can be proved as well that two plus two is five, and math is a lot of bunk. In fact, if math is not a lot of bunk, then no claim of the form "claim X can't be proved" can be proved.

    So, if math is not a lot of bunk, then, though it can't be proved that two plus two is five, it can't be proved that it can't be proved that two plus two is five.

    By the way, in case you'd like to know: yes, it can be proved that if it can be proved that it can't be proved that two plus two is five, then it can be proved that two plus two is five.

  38. higher level by Anonymous Coward · · Score: 0

    This is PRECISELY the problem with metamath.

    There needs to be higher level block that can be reused (and can always be expanded through variable substitution)

    Do we imagine programming today with assembler ?
    it is the same for formalized math.

    We need a way

    - to pack proof and add a title (for instance use in a proof "this is true by compactness".

    - to have and publish libraries of concept

    It is exactly like programming..
    Mathematician have neglected it up to now but this is a CARDINAL mistake, as it has the potential to make self adaptive lessons for instance, have automatic exercises generation etc, etc....

    This is a tremendously exciting project that can completely change the way math is learned and generate a true LEAP in our collective mathematical abilities.