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Subject: Re: Unusual Mate in 3

Author: Robert Hyatt

Date: 08:33:36 03/02/06

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On March 02, 2006 at 07:29:46, Thomas Mayer wrote:

>Hi Charles,
>
>>  Came across this position by accident browsing chess club web sites.
>>  It comes from the Duke University Chess Club. The position is
>>  1r5k/4NP1b/7K/8/6R1/8/8/8 w - - 0 1
>>
>>  Telepath found the mate in 4 but could not find the mate in 3.
>>  After some debugging I found out why!!!
>>
>>  Just before the final ply in the mate in 3, Telepath announced insufficent
>>  material which is true. But in this position you can mate with insufficient
>>  material.
>>
>>  It put such a smile on my face, I had to share it.
>>
>>  Maybe some of you have the same logic flaw in your code.
>
>well, somehow. With TBs Quark finds the mate, of course, but when I play to the
>position it says draw for Bxg8...  When I play instead of just analyzing it even
>ends the game in WinBoard with claiming draw. I wonder how many more engines
>have this problem as well... :) There are of course several other scenario
>thinkable where this problem might arise, interesting and thanks for pointing
>that out, even when it is not really strength related. Also it would be
>interesting to see if some engines / GUI act here different when TB's are
>enabled or disabled.
>
>Greets, Thomas

This is a danger of "interior node recognizers" if you use those.  It is safe to
evaluate such positions as draw in your eval, because then your search will find
the mate.  But if you try to recognize such draws at interior nodes, you
potentially have this problem...





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