Author: James Robertson
Date: 19:49:52 11/20/98
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On November 20, 1998 at 20:15:08, James B. Shearer wrote: >On November 20, 1998 at 00:47:46, James Robertson wrote: > >>On November 19, 1998 at 22:34:09, James B. Shearer wrote: >> >>> I was playing a Crafty clone on ICC and the following position arose: >>> >>>setboard r5k1/ppp1Q2p/1q4p1/8/8/2P1B3/bP4P1/4R1K1 b - - 0 24 >>> >>>The clone played qb6xb2 which loses quickly after be3-d4. I checked the >>>position after the game was over with crafty 15.15 on my k6-233. Crafty seems >>>to take an inordinate amount of time to reject qxb2 (over 100 seconds). Every >>>other program I have (cm5500, rebel8, rebel decade20, fritz4) either never >>>considers qxb2 or rejects it quickly (under 1 second). Is this a bug? >>> James B. Shearer >> >>Perhaps a null move problem (unlikely)? The mate is at ply 12 although Black >>should realise that it loses it's queen (even if it doesn't see the mate) by ply >>8. Ply 8 is when Crafty finds 1. ... c5 (after 28 seconds on my P233). GnuChess >>is another program that has problems with this position. > > Actually black gets mated or loses his queen at ply 6. This may be a >null move effect since the bad stuff happens at the end so playing a null move >will push it over the horizon (because of the reduced depth after a null move). >So perhaps R=2 means this gets pushed to ply 8, which is bad news in a bullet >game (which this was). I have seen this sort of thing before with Crafty, it >seems very dangerous to allow the null move to end the search entirely. > Also I suspect the other programs have some sort of extensions which >allow them to pick this up before ply 6. > James B. Shearer Sorry, I miscounted the plies. To get a program to analyze this under Winboard, you have to first make a move with White, and then select Computer Play Black. I made the first move with white, and then white mates on move 6, which, if counted incorrectly (doubled) makes me get 12 plies for mate, or 2 extra plies. :) James
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