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Subject: Re: Also Fritz 8.0.0.23 and Crafty 19.03 miss a mate in one!

Author: Sune Fischer

Date: 16:44:43 07/25/03

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On July 25, 2003 at 19:24:21, Eran wrote:

>On July 25, 2003 at 17:50:21, Ernst Walet wrote:
>
>>This afternoon my account on the chessbase server played a game against Rebel
>>12.  To my astonishment Rebel missed a mate in one, and got mated right away.
>>Any thoughts on this, Ed?
>>
>[D]8/8/6p1/6k1/3p2P1/4b2Q/4Bq2/7K w - - 0 151
>
>If Fritz 8 or Crafty 19.03 plays the same game instead of Rebel 12, Fritz or
>Crafty will play the same problem as Rebel 12. Please see below.
>
>So, do Fritz and Crafty have a bug for a long time?

I suspect most engines has that bug, including mine.
I've known about it for over a year, but have decided not to fix it because I
can't find a way to do it.

The reason is the engine makes the 50th move, checks the 100 ply counter and
returns the draw score.

To fix it, the engine needs to check for check mate _before_ it checks the
counter, but most engines can't do that staticly, they have to search another
ply to see the mate.

If they instead hold off (e.g. when in check) and return draw at ply 101, then
this bug is solved, but the engines will now see the 50 move rule as a 51 move
rule (actually 50,5 move rule).

I don't see a way to fix this, maybe someone has an idea?

-S.



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