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Subject: Re: The "same threat extension" as effective way to resolve horizon prob

Author: Robert Hyatt

Date: 10:54:04 10/01/03

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On October 01, 2003 at 13:00:50, Anthony Cozzie wrote:

>On October 01, 2003 at 09:08:28, Sergei S. Markoff wrote:
>>>What is the new quasy-Botvinnik extension if
>>Well. I can inform chess community about one of my quasy-Botvinnik methods.
>>I will be glad to receive your own experiment results and/or other
>>considerations about this method.
>>One of Botvinnik ideas is to determine attack/defence targets for further
>>analysis of attack/defend trajectories. One of the way to find this target is
>>null-move search. If the result of null-move search < beta we can see the move
>>which fail low search bound. This move is a current threat. For example it's a
>>threat of losing some piece.
>>During the further search in this node we can found the defending move. The main
>>idea is to extend the search if the threat moves on ply and ply+2 has the same
>>target (capturing the same piece, promotes the same pawn). I can give you
>>example if you want.
>>It's one of simpliest way to use target info. But I think we can receive more
>>improvement exploiting this idea.
>>Best wishes,
>Wouldn't this have the effect of extending lots of silly moves?
>For example, if my Queen is hanging
>BxP+ KxP (extension triggers)
>R+ KxR   (extension triggers)
>Just offhand, it seems to me like a good Q-search should fix these problems.

See my other post on this first.  But this is a known exception.  IE using
the null-move threat extension (Chrilly) you would extend if at ply N-1 you
play QxQ and force the trade of queens.  At the next ply, a NULL move search
will definitely fail low because the opponent will move the queen away.  And
capturing the queen will likely fail high as it restores material balance.

This is just an exception that has to be handled and not extended.  IE if the
best move is a capture of the piece moved at the previous ply, forget about the
extension as it is an obvious recapture that doesn't need any special extension
(perhaps excepting the recapture extension if you do that.)

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