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Subject: Re: Hashing rules

Author: Uri Blass

Date: 22:26:58 04/05/03

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On April 05, 2003 at 22:46:58, Robert Hyatt wrote:

>On April 05, 2003 at 14:02:09, Russell Reagan wrote:
>
>>Regarding hashing of the en passant square and castling rights, I have a few
>>questions. I think I understand this now. I'd just like some verification.
>>
>>You should only hash the en passant square if it is possible for an enemy pawn
>>to execute the en passant capture. This means, ideally, that if there is a pawn
>>present to make the capture, but it is pinned and cannot legally make the
>>capture, that you should not hash the en passant square. Is this correct?
>
>Correct, but it might be too expensive to determine if the pawn is
>pinned.  It is good enough to simply note that a pawn _can_ be captured
>EP only if it has advanced two squares and there is an enemy pawn on an
>adjacent file in the right place.

I agree that it is good enough and the point is that the biggest errors that you
can do in rare cases is considering repetition as no repetition and
not claiming draw because of repetition of the same position 3 times
because of believing that it only repeated twice.

Uri



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