Author: Tim Foden
Date: 00:04:51 02/07/04
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On February 06, 2004 at 22:46:15, Ricardo Gibert wrote: >On February 06, 2004 at 13:48:48, Jaime Benito de Valle Ruiz wrote: > >>This endgame study can be game following the sequence >> >>1.Bd1 g1Q 2.Bxa4 Qc1 3.Bxd7 h5 4.Be8 h4 5.Ba4 Line >> >>[d] 8/3p4/p6p/k2N3B/p7/K6p/PP4pP/8 w - - 0 1 >> >>Many engines (Fritz 8, Hiarcs 8, Ruffian 1.01) cannot win this endgame, probably >>due to the well known null-move problem for extreme and rare positions such as >>this. > >These programs have an obvious bug in their implementation of null move. They >should not be using stalemate as a fail high for a null move. Stalemate is tempo >dependent thing and null move mucks up the tempi. You can think of stalemate as >an obvious sort of zugzwang. Note, that it doesn't matter which side gets >stalemated after a null move. The stalemate should be treated as a fail low for >the null moving side regardless. No, I agree with Uri here, its blacks queen move which is in Zugzwang which is the problem. At c1 it's stopping the b4+ move, once it moves, black has lost. The programs go for the stalemate because it's the best that they can see because they don't see that the queen has to move. They key to this position seems to be that there is a strong king attack on black... blacks king cannot move. And although b4+ is a long term threat for mate. If a program sees this it should not use null move for black in this position, and that would solve the problem. Cheers, Tim. [BTW GLC has no clue here, unless I turn null-move off :) This position goes in my list of zugzwangs to be dealt with]
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