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Subject: Re: SEE for forward pruning in the Q. search - I'm confused!

Author: Robert Hyatt

Date: 15:20:32 08/11/99

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On August 11, 1999 at 16:12:07, Tom King wrote:

>I must be missing something obvious with using SEE to prune
>in the Q. search. If I understand right, "losing" captures
>(according to the SEE) are pruned right out. But I fail to
>see how this won't screw up big time.
>
>Let's take an example. Now assume we have a white bishop on G5
>and a black knight on F6, and the knight is protected by a pawn on G7.
>Now the SEE might well assume that BxN is a loser (assuming that
>the bishop is worth a fraction more than the knight), because
>after BxN, gxB, white has lost a bishop for a knight. But it
>might be that this is in fact a very good capture, because it
>destroys black's kingside. And a program with the SEE Q. pruning
>might not want to play this? Am I missing something obvious
>here?
>
>Cheers
>Tom

First, my SEE won't overlook such a move, because materially, a B is worth
exactly the same as a N.  But even worse, suppose that after you play BxN,
rather than using that overloaded pawn to retake, leaving the other piece
hanging, instead I slide my rook over to f8, pinning your bishop on your king.

So if you try BxN, with the hope that it wins material, you can be wrong.  If
you don't, you can be wrong.  Two wrongs don't make a right.  :)

So take the speed and run.  :)



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