Firstly, I am not the poster of the solution, but I did solve it independently last night. I'm in Indonesia on holiday. I just logged on this morning to see if I had it right. It took me about 1.5 hrs. Having a chess board might have helped:) Firstly, I reasoned it was probably black that gave mate as the problem did not state that it was white. I did spend some time searching for a white solution, but not much. I tried to block in the white king with its own pieces, but this takes too long. There were only a few ways to do this and none gave a valid mate. The move e2-e4 was not helpful for this. Castling seemed a waste of time. Took too long and the rook ended in a very inconvenient position. The main problem was to get the knight across fast enough. It was taking 3/4 moves. Then I tried to help out by bringing the rook to a more convienient place. Closer but still no luck. Then I reasoned that in such a difficult puzzle the move e2-e4 was probably important, but why? I didn't think it possible to mate with knight only so I tried bringing out another piece and trying a discovered check. But this takes two moves which was too long, but how else could it be done? I had ealier found it helpful to have the black night remove an annoyingly positioned white pawn, that lead to a "solution" that wasn't valid chess - white ignores check. Well what if white were to remove a black pawn... But now it took too long for white. If black were to take the white piece taking the pawn it would help, but it was still taking two moves to get the piece somewhere useful. What this puzzle really needed I thought were some queens whizzing about the board. At this point the e1-e8 line looked very suspicious. And armed with the idea of white removing a black pawn and the black knight removing an awkward white pawn it all fell into place. Of course it wasn't so straight forward, but that was generally how I did it. (I skip the part where I tried to figure out how long it would take to write and run a program to brute force it - a long time, and the frustating bit at the end where I forgot the solution) I'm not a good chess player. I think luck may have had something to do with it for me.
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Firstly, I am not the poster of the solution, but I did solve it independently last night. I'm in Indonesia on holiday. I just logged on this morning to see if I had it right. It took me about 1.5 hrs. Having a chess board might have helped :) Firstly, I reasoned it was probably black that gave mate as the problem did not state that it was white. I did spend some time searching for a white solution, but not much. I tried to block in the white king with its own pieces, but this takes too long. There were only a few ways to do this and none gave a valid mate. The move e2-e4 was not helpful for this. Castling seemed a waste of time. Took too long and the rook ended in a very inconvenient position. The main problem was to get the knight across fast enough. It was taking 3/4 moves. Then I tried to help out by bringing the rook to a more convienient place. Closer but still no luck. Then I reasoned that in such a difficult puzzle the move e2-e4 was probably important, but why? I didn't think it possible to mate with knight only so I tried bringing out another piece and trying a discovered check. But this takes two moves which was too long, but how else could it be done? I had ealier found it helpful to have the black night remove an annoyingly positioned white pawn, that lead to a "solution" that wasn't valid chess - white ignores check. Well what if white were to remove a black pawn... But now it took too long for white. If black were to take the white piece taking the pawn it would help, but it was still taking two moves to get the piece somewhere useful. What this puzzle really needed I thought were some queens whizzing about the board. At this point the e1-e8 line looked very suspicious. And armed with the idea of white removing a black pawn and the black knight removing an awkward white pawn it all fell into place. Of course it wasn't so straight forward, but that was generally how I did it. (I skip the part where I tried to figure out how long it would take to write and run a program to brute force it - a long time, and the frustating bit at the end where I forgot the solution) I'm not a good chess player. I think luck may have had something to do with it for me.