Author: James B. Shearer
Date: 17:15:08 11/20/98
Go up one level in this thread
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
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