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Subject: Re: Restricting extensions

Author: Volker Böhm

Date: 15:19:04 09/12/04

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Hi Scott,

the idea behind a check-extension is not only to find great attacks beginning
with a checking move. One other major idea is to prevent horizont effects.
Example: you give away a piece for a really good attack. But the opponent has
the opportunity to give you some checks, pushing the really good attack out of
sight. Extending the checks in positions below alpha helps to fix this problem.

I never found a good idea to reduce check extension.

By the way why do you extend on promotion? I never heard anyone doing it. Thus
maybe the reduction will work here (the more reduction the better :-)

A reduction that gained a little was the pawn-pushed-to-row-7 extension that I
only extend, if the pawn on row 7 cannot be taken without material loss (SEE >=
0).

Something that could be tested (I think) is the reduction of the
take-back-extension that is perhaps not that usefull if far away from the
search-window.

On the other hand: maybe futility, extended futility and razoring is a better
concept than reducing extensions by comparing against alpha and beta. Thus I
think you should test your ideas only if you have at least futility.

Greetings Volker



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