Computer Chess Club Archives




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

Author: Omid David Tabibi

Date: 08:43:10 11/20/02

            ICGA Journal, Vol. 25, No. 3, pp. 153-161, September 2003

                          Verified Null-Move Pruning

                    Omid David Tabibi and Nathan S. Netanyahu


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.

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.

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