Author: José Antônio Fabiano Mendes
Date: 14:47:43 04/04/00
Go up one level in this thread
On April 03, 2000 at 11:58:30, Dave Gomboc wrote: >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 The "Troitzky line" for the ending two knights against a single pawn [1934] [D]8/8/1p4p1/1Np2pN1/p1NppN1p/N2NN2N/8/8 w - - A white knight blocks a black pawn. Source:"test Tube Chess",A.J.Roycroft,1972,page 200,Stackpole Books JAFM
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