After the chess puzzle in my previous post, there was a lot of discussion about chess programs, but no one seems to have attempted the puzzle itself :-) Its a difficult puzzle, but the solution is also really beautiful and it helps to explain why engines don’t find it. So I thought I would devote another post to it. If you want to try the puzzle yourself, please stop reading here.
To recap, the initial position is the one on the left. With white to play, the correct continuation is 1.Qc8 Kg8 2. Bc7!
This is the move that engines cannot find, since it involves a immediate huge loss of material and the payback is only because of a positional novelty that manifests itself several moves down the line. So presumably, most algorithms just prune this move. After this move is played, engines can find the continuation, which is: 2. …Qxc8 3.gxf7+ Kh8 4.Be5 Qc5 5.Bb2 Nc7 6.Ba1
This brings us to the position in the second figure below. Now Black is not, strictly speaking, in zugzwang. But Black will be in zugzwang after 4 moves! Play continues 6. … a4 7. Bb2 a3 8.Ba1 a2 9. Bb2 a1=Q 10. Bxa1 Qe5+ 11. Bxe5 Nd5+ 12. Ke6+ Nf6 13. Bxf6#
