Author: Dave Gomboc
Date: 08:58:30 04/03/00
Go up one level in this thread
On April 03, 2000 at 11:53:34, KarinsDad wrote: >On April 03, 2000 at 11:44:44, blass uri wrote: > >>On April 03, 2000 at 10:54:21, KarinsDad wrote: >> >>>On April 03, 2000 at 06:10:21, Jeremiah Penery wrote: >>> >>>>There is a problem with tablebases. >>>> >>>>No, they don't produce wrong answers. And no, they don't make engines play >>>>weaker. The problem is that engines would rather be -9 and not in TBs than see >>>>mate against itself and be in TBs. I have one good example, from a game my >>>>modified Crafty played on ICC, and I may try to find it, if possible. But I do >>>>remember what happened: >>>> >>>>I had something like a knight and a pawn, and my opponent had 2 knights and a >>>>pawn, about to promote. I had the choice to let him promote, and have a score >>>>of about -9. I would easily lose. My other choice was to sacrifice my knight >>>>for his pawn, and enter a lost KNNKP endgame, somewhere around Mate in 75. I >>>>would not easily lose this, unless my opponent had the TB, in which case it >>>>could be a draw by 50-moves. >>> >>> >>>Excuse me, but what am I missing? >>> >>>Isn't a KNNKP ending almost always a draw (assuming nothing special) if the side >>>with the pawn wants it to be? Cannot the side with the pawn force the draw >>>(regardless of 50 move rule) since KNNK is a draw? >> >>No >>The side with the two knight can sometimes win against a pawn because the side >>with the 2 knights can avoid stalemate when there is a pawn because the pawn can >>move and cannot avoid stalemate if he use the same plan when there is no pawn. >> >>Uri > >Huh? > >The side with the pawn pushes the pawn. If the other side captures, it is KNNK. >If the other side blocks it with a knight, then it is KNK (effectively). The >side with the pawn sits his king in the middle of the board and jumps back and >forth. If the side with the knights comes after the king, then the side with the >king pushes the pawn again. > >This still seems like it can be a forced draw by the side with the pawn. > >Now, of course, if you have some special position where the two knights can mate >the opposing king because it is trapped against the edge due to his own pawn, >then I can understand that it COULD happen. But that does not seem to be the >case in the example sited since he is talking about a forced mate in 75. > >KarinsDad :) There are a large percentage of wins in KNNKP. The pawn must be blockaded before it gets too close to the promotion square. The specific distance depends on the file it is on. IIRC, this was extremely well-analyzed by a human long before a tablebase was generated for it. Dave
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