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Subject: An improvement to null move search

Author: Tord Romstad

Date: 01:06:38 04/07/04


The following idea is still untested, but unless I am missing something it
is guaranteed to reduce the number of nodes without any risk.  The idea is
fairly obvious, and I am sure some of you are already using it, but I still
don't think it is widely known.

At a node where the remaining depth is sufficiently big that a null move
would not drop us directly into the qsearch, and beta > DRAW_SCORE, avoid
doing a null move search if the move leading to the node was a reversible
move.  The point is that we know that the null move search is a waste of
time in this case.  After the null move, the opponent can just reverse
his move, with a repetition draw score.

Tord



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