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Subject: Re: Verified Null-Move Pruning, ICGA 25(3)

Author: Miguel A. Ballicora

Date: 11:29:52 11/20/02

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On November 20, 2002 at 11:43:10, Omid David Tabibi wrote:

>            ICGA Journal, Vol. 25, No. 3, pp. 153-161, September 2003
>                          Verified Null-Move Pruning
>                    Omid David Tabibi and Nathan S. Netanyahu
>                                   Abstract
>In this article we review standard null-move pruning and introduce our extended
>version of it, which we call verified null-move pruning. In verified null-move
>pruning, whenever the shallow null-move search indicates a fail-high, instead of
>cutting off the search from the current node, the search is continued with
>reduced depth.

Nobody thought about this before? Never published? I cannot say that I am going
to try it because... I've been doing this with Gaviota since the beginning :-).
It looked logical to me. It avoids most of the problems with zugzwangs IMO. Nice
to see a proof that it is worth it, though. It is very similar, IMHO, to what
some other people do, which is try at reduced depth (first) to see if the
nullmove search is worth doing it. I think that YACE does that from Dieter's
comment. I believe that YACE's approach is better but I never bothered to check.
Thanks for the paper, I have problems downloading the pdf, I will try later the
other files.


>Our experiments with verified null-move pruning show that on average, it
>constructs a smaller search tree with greater tactical strength in comparison to
>standard null-move pruning. Moreover, unlike standard null-move pruning, which
>fails badly in zugzwang positions, verified null-move pruning manages to detect
>most zugzwangs and in such cases conducts a re-search to obtain the correct
>result. In addition, verified null-move pruning is very easy to implement, and
>any standard null-move pruning program can use verified null-move pruning by
>modifying only a few lines of code.
>zipped pdf:
>gzipped postscript:

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