Author: Vasik Rajlich
Date: 04:36:57 06/05/05
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On June 04, 2005 at 14:06:48, Rémi Coulom wrote: >On June 04, 2005 at 13:07:29, Ernest Bonnem wrote: > >>[D]6n1/3p4/8/1P1Pk1n1/4P3/B5K1/8/8 w - - >> >>White to win >> >>Here Shredder 9 UCI cannot find the "simple" b6! even at depth 36/61 (searching >>more than 2 hours on my computer) >> >>b6 is found almost immediately by all other programs I tried (Fritz 7, Tiger, >>Pharaon,...) >> >>Has anybody an explanation ? > >null move hides a zugzwang, maybe. After b6 Nxe4+ Kh4 Nd6 Bxd6+ Kxd6 Kg5, black >is in zugzwang, if I understand correctly. > >It is really not very wise to do the null move in such a situation. I would find >it strange if Shredder has such a hole. So Shredder's problem may be a little >more subtle. It is hard to guess. > Yes, exactly, after 1. b6 Nxe4+ 2. Kh4 Nd6 3. Bxd6+ Kxd6 4. Kh4 the following zugzwang arises: [D] 6n1/3p4/1P1k4/3P2K1/8/8/8/8 b - - Even here I still needed the engine to explain it to me - the point is that 1. .. Ne7 is refuted with 2. b7+ Kc7 3. d6+. This is extremely unusual, everything falling right into place. In Rybka I switch of null move whenever 1) there are no major pieces on the board 2) neither side has more than one minor piece. This however is way too conservative - in principle what Shredder is doing must be better. Vas >Rémi
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