Computer Chess Club Archives




Subject: Re: Double Null move?

Author: Uri Blass

Date: 14:00:34 07/13/01

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On July 13, 2001 at 16:50:26, Uri Blass wrote:
>If you search to clearly reduced depth(for example before normal search with
>null move pruning to depth d when d>=6 you search without null move to depth
>d/2-2) then you may be less than 1% slower.

I mean the following:
normal null move search to depth d and only if there is a cutoff
to do searching without null move to depth d/2-2 to verify no zunzwang.

There are also other ways to do it with the double null move.

I understand that the idea of the double null move is simply the assumption that
you cannot play 3 null move in a row and you search the game when the sides can
avoid moving but not 3 times in a row so practically the result is the same
result if you search deep enough and a mate in 2 with zunzwang can be solved by
Ra6 bxa6 b7# can be solved when the main line is
Ra6 null null bxa6(now black cannot avoid moving by the rules) b7#.

null may mean 3 plies so practically the program may need 1+3+3+1 plies to see
mate in 2 with zunzwang.


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