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Subject: Re: Crafty-IsiChess,CCT4,r11 ==> A move to avoid?

Author: Gerd Isenberg

Date: 15:43:01 01/30/02

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On January 30, 2002 at 17:02:28, Miguel A. Ballicora wrote:

>>I do not know what a confirmatory search is (I guess I can imagine, something
>like YACE) but I think of 3 possible ways:
>1) reduce depth, rather than pruning (Gaviota)
>2) double nullmove (Diep)
>3) apply only nullmove when depth is < x plies. x could be something like 7 etc.
>This one I think is Crafty, according to some posts in the past (IIRC).
>When you search so deep, there is one point where moves close to the root are
>not nullmoved anymore. Solution to nullmove problems are just delayed.

To 3) x is constantly 2.

When i get a nullmove fail high and some other depth related conditions  met, i
use a reduced search to confirm the fail high or to detect zugzwang. When this
confirmation search (same depth reduction as nullmove search: depth-R-1, but
nice to play with another R) goes less beta, doing nothing is the best. Zugzwang
is detected and the "normal" search continues, instead of pruning.
Zugzwang detection is also stored in hash tables and may disable nullmove in
further iterations.

I imagine, that it's most similar with Vincent's double nullmove. But the
control flow and the search depth of the second nullmove search are different.


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