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Subject: Re: Recapture extension in Crafty

Author: Robert Hyatt

Date: 06:02:06 07/25/01

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On July 25, 2001 at 01:21:26, Jouni Uski wrote:

>Can somebody explain, what is recapture extension meaning. Now it's on in 18.10
>and may be Crafty has reached agains the level of 17.14!?
>
>thanks Jouni


It was only disabled for one version I think...  But the idea is that one
common way to "horizon-effect" some tactical problem is to play a move (like
a check) that forces a reply by the opponent.  Do this a couple of times in
the search, and the "problem" gets pushed off beyond the search horizon and
it disappears.  Only to come back after you play the first forcing move and
the opponent plays the forced response...

A capture like BxN can be used to do the same thing, since it is necessary to
take time out from the main tactical theme and recapture the bishop to maintain
material equality.  That burns up two plies of search.  Crafty (and most other
programs) extend the search under certain controlled conditions to try to
reduce the horizon effect of such capture/recapture move pairs...



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