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Subject: Re: Crafty-IsiChess,CCT4,r11 ==> A move to avoid?

Author: Gerd Isenberg

Date: 14:59:18 01/30/02

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On January 30, 2002 at 16:11:07, Uri Blass wrote:

>>If i use Nullmove here, but no confirmation-Search, IsiChess finds Nxd5 in about three minutes.
>
>I do not understand it.
>
>How is it possible to find Nxd5 with null move pruning without confirmation
>search?
>It seems impossible to do it.
>
>after searching the line Nxd5 Rxd5 Re6 that is not the main line the computer is
>going to find that there is no threat and prune the line.
>
>I expect normal null mover never to find it even after 3 years because it is
>going to say the following:
>
>1)The score after moves like Rd8 or Ne2 is about +1 for white
>
>2)Nxd5 Rxd5 Re6 has no threat in other words the score after Nxd5 Rxd5 Re6 when
>it is black to move is better than +1 for white and the conclusion is that the
>computer does not need to search Nxd5 Rxd5 Re6
>
>3)The score after Nxd5 Rxd5 not Re6 is also better than 1 pawn for white
>
>conclusion Nxd5 is worse than Rd8 and is not the right move.
>
>Uri

Good question.
I am not quite sure and i may have a closer look at it. But i think the
following:

In my Nullmove implementation there are some conditions to hit, disabling
nullmove observation. Some of this conditions are depending from a "skipNull"
flag, may be set by eval just before.

It is set most likely in blocked pawn positions. Some danger and mate flags and
king-king distance are also a matter.

I use some easy generated Bitboards for Pawns, blocked by enemy Pawns (Widder)
and Backward Pawns. If most of the pawns are Widder or backward but no Hebel
(pawn may capture pawn), the pawn position is considered as blocked.

Gerd





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