Whether this is a valid inference depends on the definition of 'universal'; the problem here is that Pratt appears to be using a different definition from the one that the prize committee and the proof adopt. The inference may be incorrect with certain definitions of 'universal'; however, it is correct with other definitions. My point is that the counterexamples that Pratt gives to the inference are incorrect; that does not, of course, mean that the inference itself is correct, but it means that looking into where the problems with the counterexample came from is worth doing, and it appears to be a misconception between systems interacting backwards and forwards, and preprocessors. It seems to me that most general definitions of 'universal' will cause the inference in question to be correct (there is at least one definition which includes the inference as part of the definition itself, that is 'A system is universal if it can emulate any Turing machine if given an appropriate initial condition encoded using a non-universal system', although there is some circular reasoning involved in that definition).
This argument and Pratt's argument that the universality proof are incorrect both share the same flaw; see the response linked in the update of the original story for more details. Yes, a system consisting of two push-down automata that can communicate back and forth is universal. However, the proof of the universality of the 2,3 Turing machine in question doesn't set up a system where two systems can communicate back and forth; instead, the output of one is used as the input of the other, and there is no communication in the other direction. If one PDA is used as an encoder for another, the resulting system is not universal. The definition of universality in the original prize that was agreed on by the judges basically said that in the case of obviously simple encoders, if an encoder+system together are universal than the system itself is. The encoder used in the proof is not obviously simple (as it takes up several pages in the proof) but is clearly not doing any sort of universal calculation itself or engaging in part of such a calculation.
The real problem here is that with other definitions of 'universal', the system might indeed not be universal; the definitions are important in such cases. (For instance, a definition that restricted the initial condition to be finite and surrounded by nothing but yellow on the tape would result in the system being non-universal, but this definition is too restrictive to be useful.) Changing the definition of 'universal' is likely to result in changes to what is universal and what isn't, although it seems likely that the 2,3 Turing machine in question is well on the universal side of that edge (although not as far as some other systems). Even systems such as rule 110 that are generally accepted to be universal would be non-universal if a non-repeating finite initial condition was mandated by a definition of universality.
So in short, nothing has been disproven, the machine is still universal, and the headline is wrong.
The definition of 'universal' used in for the competition is not precisely defined, but rather skirted around; see the section "Uses of the Term Universality" (which for some reason doesn't have an anchor, so I can't link to it directly) in the technical details of the prize. Instead of 'halting', the Turing machine in the proof exhibits behaviour that can be considered to be equivalent to halting; there are points in the tape where if the Turing machine moves to their right, it never goes back to their left again, so the information there is preserved as long as the machine is running, and particular sorts of configurations of the section between two such points can be interpreted as saying that the machine has 'halted' (if it generates such a configuration, then every time one of those points is passed the next section will also have a similar configuration, and so on for ever, so the machine is no longer doing any useful computation but instead just doing the equivalent of a very busy busy-wait where it recalculates what it's already calculated over and over again).
There are enough problems with arguments about whether a vote should be counted or not as it is, in any system. With optical scanning of a ballot paper, surely there will be arguments about whether what the scanner counts as a vote or not is actually the correct definition of what is a vote or not? The voting system is likely to be attacked by people who disagree with its definitions whatever it is.
Actually, it is possible to get rid of the 'Windows Tax'; if you don't accept the licence agreement on Windows and then uninstall it, it's possible to get a refund (see this BBC News story). Presumably this applies whether you want to install Linux, an older version of Windows, or even another OS.
It could be more difficult than usual; IANAL, but one thing that often happens after a patent infringement claim is a counter-claim with another patent, and then a cross-licensing agreement is often reached to settle the situation. However, this may be a case of patent trolling, where this means of protection doesn't work because the company who owns the original patent doesn't actually make anything related, and therefore cannot have any related patents. Of course, attacking the patent itself or showing that it's inapplicable still work, I think (and hope). Besides, software patents can't be enforced or don't exist in many countries (particularly in Europe), so a patent attack would be unlikely to get rid of Linux altogether.
The data in the linked Wikipedia user subpage aren't necessarily showing an accurate view of the situation; see http://en.wikipedia.org/wiki/User_talk:Dragons_flight/Log_analysis#More_data for some more data that was generated by me (and in the section below, data by another user) to try to corroborate or raise doubts about the data used to make the claims. My data shows that edit rate was dropping off from about April to August, but is possibly picking up again (although there isn't really enough data since August to tell for certain) - note that my data takes into account all edits, even reverted edits, deleted edits, and edits not to articles. The data (due to Wikipedia user Gmaxwell) in the section below that take only edits to articles (which the software thinks of as 'namespace 0', to explain the title of that section) into account show much the same pattern. Gmaxwell has also raised doubts about the sampling method that Dragons flight used. So although the current edit rate is lower than the record edit rate, it's certainly reasonable to believe that new records may be set in the future.
Slashdot Mirror
Whether this is a valid inference depends on the definition of 'universal'; the problem here is that Pratt appears to be using a different definition from the one that the prize committee and the proof adopt. The inference may be incorrect with certain definitions of 'universal'; however, it is correct with other definitions. My point is that the counterexamples that Pratt gives to the inference are incorrect; that does not, of course, mean that the inference itself is correct, but it means that looking into where the problems with the counterexample came from is worth doing, and it appears to be a misconception between systems interacting backwards and forwards, and preprocessors. It seems to me that most general definitions of 'universal' will cause the inference in question to be correct (there is at least one definition which includes the inference as part of the definition itself, that is 'A system is universal if it can emulate any Turing machine if given an appropriate initial condition encoded using a non-universal system', although there is some circular reasoning involved in that definition).
This argument and Pratt's argument that the universality proof are incorrect both share the same flaw; see the response linked in the update of the original story for more details. Yes, a system consisting of two push-down automata that can communicate back and forth is universal. However, the proof of the universality of the 2,3 Turing machine in question doesn't set up a system where two systems can communicate back and forth; instead, the output of one is used as the input of the other, and there is no communication in the other direction. If one PDA is used as an encoder for another, the resulting system is not universal. The definition of universality in the original prize that was agreed on by the judges basically said that in the case of obviously simple encoders, if an encoder+system together are universal than the system itself is. The encoder used in the proof is not obviously simple (as it takes up several pages in the proof) but is clearly not doing any sort of universal calculation itself or engaging in part of such a calculation.
The real problem here is that with other definitions of 'universal', the system might indeed not be universal; the definitions are important in such cases. (For instance, a definition that restricted the initial condition to be finite and surrounded by nothing but yellow on the tape would result in the system being non-universal, but this definition is too restrictive to be useful.) Changing the definition of 'universal' is likely to result in changes to what is universal and what isn't, although it seems likely that the 2,3 Turing machine in question is well on the universal side of that edge (although not as far as some other systems). Even systems such as rule 110 that are generally accepted to be universal would be non-universal if a non-repeating finite initial condition was mandated by a definition of universality.
So in short, nothing has been disproven, the machine is still universal, and the headline is wrong.
The definition of 'universal' used in for the competition is not precisely defined, but rather skirted around; see the section "Uses of the Term Universality" (which for some reason doesn't have an anchor, so I can't link to it directly) in the technical details of the prize. Instead of 'halting', the Turing machine in the proof exhibits behaviour that can be considered to be equivalent to halting; there are points in the tape where if the Turing machine moves to their right, it never goes back to their left again, so the information there is preserved as long as the machine is running, and particular sorts of configurations of the section between two such points can be interpreted as saying that the machine has 'halted' (if it generates such a configuration, then every time one of those points is passed the next section will also have a similar configuration, and so on for ever, so the machine is no longer doing any useful computation but instead just doing the equivalent of a very busy busy-wait where it recalculates what it's already calculated over and over again).
It is possible on Wikipedia with a slash (although %20 is needed rather than space because space is an invalid character in URLs): http://en.wikipedia.org/wiki/Special:Search/Search%20terms Unfortunately, Special:Search didn't even exist until April 2004, so this feature can't possibly be prior art as it can't have existed in this form before Special:Search.
There are enough problems with arguments about whether a vote should be counted or not as it is, in any system. With optical scanning of a ballot paper, surely there will be arguments about whether what the scanner counts as a vote or not is actually the correct definition of what is a vote or not? The voting system is likely to be attacked by people who disagree with its definitions whatever it is.
Actually, it is possible to get rid of the 'Windows Tax'; if you don't accept the licence agreement on Windows and then uninstall it, it's possible to get a refund (see this BBC News story). Presumably this applies whether you want to install Linux, an older version of Windows, or even another OS.
It could be more difficult than usual; IANAL, but one thing that often happens after a patent infringement claim is a counter-claim with another patent, and then a cross-licensing agreement is often reached to settle the situation. However, this may be a case of patent trolling, where this means of protection doesn't work because the company who owns the original patent doesn't actually make anything related, and therefore cannot have any related patents. Of course, attacking the patent itself or showing that it's inapplicable still work, I think (and hope). Besides, software patents can't be enforced or don't exist in many countries (particularly in Europe), so a patent attack would be unlikely to get rid of Linux altogether.
The data in the linked Wikipedia user subpage aren't necessarily showing an accurate view of the situation; see http://en.wikipedia.org/wiki/User_talk:Dragons_flight/Log_analysis#More_data for some more data that was generated by me (and in the section below, data by another user) to try to corroborate or raise doubts about the data used to make the claims. My data shows that edit rate was dropping off from about April to August, but is possibly picking up again (although there isn't really enough data since August to tell for certain) - note that my data takes into account all edits, even reverted edits, deleted edits, and edits not to articles. The data (due to Wikipedia user Gmaxwell) in the section below that take only edits to articles (which the software thinks of as 'namespace 0', to explain the title of that section) into account show much the same pattern. Gmaxwell has also raised doubts about the sampling method that Dragons flight used. So although the current edit rate is lower than the record edit rate, it's certainly reasonable to believe that new records may be set in the future.