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Subject: Re: Null move generalization

Author: Uri Blass

Date: 13:32:47 04/17/02

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On April 17, 2002 at 16:09:27, Dann Corbit wrote:

>On April 17, 2002 at 15:43:23, Jesus de la Villa wrote:
>
>>
>>Have someone defined the general rule(s) where null move
>>is unable to find simple combinations?, and if so, which
>>are those rules ?
>>
>>"Obviusly" is more expensive to check it than to not
>>use Null Move.
>
>There are times you simply must turn null move off or disasters will happen.
>
>When the board gets sparse, turn it off.
>
>If you are in check, turn it off.
>
>If you are already searching with null move, additional null move pruning [for
>subsequent plies] is questionable.
>
>If you see a checkmate threat during the null move search, turn it off or
>extend.
>
>Null move will not remove the ability to find simple combinations.  It only
>delays it.  But it might delay it enough that you will not find it in a
>reasonable time.

Null move may removes the ability to find simple combinations when zunzwang is
involved.

It happens to a lot of programs that do not use zunzwang detection(I think that
crafty is one of them and at least it was the case in the latest version that I
checked).

Uri



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