Author: Sune Larsson
Date: 07:58:58 03/01/01
Go up one level in this thread
On March 01, 2001 at 09:48:42, Vincent Diepeveen wrote: >On February 28, 2001 at 17:35:48, Sune Larsson wrote: > >>On February 28, 2001 at 16:47:27, Bertil Eklund wrote: >> >>>On February 28, 2001 at 16:23:35, Sune Larsson wrote: >>> >>>> >>>> [D]8/5b2/p2k4/1p1p1p1p/1P1K1P1P/2P1PB2/8/8 w - - 0 1 >>>> >>>> >>>> This is one of Averbakh's positions from 1954. >>>> It's a typical winning position in a good versus bad bishop ending. >>>> The black pawns on h5, f5, d5 and a6 are vulnerable and curtail the >>>> movements of the black bishop. To seal black's fate, all white need to do >>>> is lose a move. That is - repeat the initial position with black to move. >>>> This may be accomplished as follows: >>>> >>>> 1.Be2 Be8 [1.-Bg6 2.Bd3 Bh7 3.Bf1 leads to instant zugzwang, be it after >>>> 3.-Bg6 4.Bg2 Bf7 5.Bf3 or after 3.-Bg8 4.Be2 Bf7 5.Bf3] >>>> >>>> 2.Bd3 Bg6 3.Bc2 Bh7 4.Bb3! Bg8 5.Bd1 Bf7 6.Bf3! and so on >>>> >>>> >>>> Test: The above position is won for white so your program should be able >>>> to win it. The evals should differ distinctly between white and black. >>>> >>>> Sune >>> >>>Hej! >>> >>>Nimzo8 sees it immediately with a score of more then +2. >>>It also sees 1.Bg2 as winning with about the same score. >>> >>>Bertil >> >> Okej, it's a bit hard to find a good balance, when choosing these positions. >> If they are too easy some people just complain - if they are too hard >> almost noone answers...;) >> >> Sune > >The big problem is to find correct positions. Every position i always >get i have to double check things. Majority of all positions a few >tactical extensions find it already 100x faster. > >Your rook position was very cool though. The bad bishop on g3 i had >already implemented quite some time ago :) > >The problem here is that in a normal position a single bad placed pawn >can lose, nearly all programs realize that now. > >however this position is more complicated from human viewpoint as the black >king is doing a great job, so you need more weaknesses and need a zugzwang >here. > >How to tell my program that it only wins this position if it can create >a zugzwang? > >So the basic fault here of the chessplayer is the assumption that it is a >bad bishop position. it's in fact a zugzwang position. >for a single zugzwang you need a few plies of search that's it. > >Cool for my double nullmove to show its correctness, but no big deal >really :) Very relevant remarks, thanks! I also noticed this double thing very clearly in the following position: white: Kb4, Nc5, Pd4,e5,g5 black: Kb6, Bf7, Pd5,e6,g6 Now this is a good knight vs bad bishop ending - and white wins. But the second factor is the king's positions! Just try to shift them to: white Kb3 black Kb5...
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