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

Author: Omid David Tabibi

Date: 11:42:04 11/20/02

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On November 20, 2002 at 14:29:52, Miguel A. Ballicora wrote:

>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.

Plenkner (1995) suggested using a reduced depth search in order to detect
zugzwangs. However, it is the first time a reduced depth search is used to
improve the tactical strength.

The continued search after a fail-high report enables detecting many moves which
wouldn't have been detected in standard null-move pruning, due to the horizon


>>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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