Author: Thomas Mayer
Date: 12:27:17 03/02/06
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Hi Bob, On March 02, 2006 at 11:33:36, Robert Hyatt wrote: >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. > 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... well, in fact it is not my "interior node recognizer". It is my draw function. Whereas the INR-function is aware of that possibility, my draw function has no idea - and it a) produces also cutoffs in the tree and b) is responsible for the draw claim... funny... I did take so much care about my internal node recognizers not to give back wrong results (even checking them with TBs) and then the draw function is the problem... :) Greets, Thomas
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