Author: Slater Wold
Date: 14:08:59 04/23/02
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On April 23, 2002 at 12:40:09, Robert Hyatt wrote: >Here is an endgame position posted a week or so: > >[D]1b6/8/8/7p/6k1/6P1/8/6K1 w - - 0 1 > >This endgame causes some problems to Crafty because it doesn't recognize >stalemate in the q-search. > >The problem here is that black can't win, obviously. Bishop + wrong rook >pawn. But if black could somehow zugzwang white into moving his g-pawn so >that black could play hxg4, then this becomes an easy win for black. > >Crafty's endgame evaluation understands that with the wrong rook pawn, this >is drawn, and here it concludes "black can't win" which is correct. However, >as the search progresses, the trick to break my eval term is to get the white >king on h1, with the black king at h3, and the black bishop at a7. Now the >white king can't move and white is forced to play g4 where black follows up >with hxg4 and the eval now says black wins. The problem with this position >is that white is _still_ stalemated (white king at h1, black king at h3, >black bishop attacking g1 so that the king can't move. It becomes easy for >a full-width search to shuffle pieces around, then force the zugzwang (almost- >zugzwang) to happen so that hxg4 happens at the last ply of full-search, or >at the first ply of the q-search. Either case results in a stalemate, but >since I don't try all legal moves in the q-search, I don't notice this. The difference between me and Bob: I'd just download the 5 man tables and call the problem "solved". :D Nice find Bob. It might not be much, but with 1B possible positions in chess, perhaps this will be that little piece of knowledge that wins 1 important game. And then it's all worth it. Good job. ;)
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