Author: blass uri
Date: 10:09:09 04/03/00
Go up one level in this thread
On April 03, 2000 at 13:07:08, blass uri wrote: >On April 03, 2000 at 12:11:53, KarinsDad wrote: > >>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 >> >>Ok, so what you are saying is that if the pawn is sufficiently advanced, then >>the side with the pawn can force the draw. Otherwise, the side without the pawn >>can first blockade the pawn and later put the opposing king in check often >>enough so that even though the pawn can push, the king is forced into the corner >>and checkmated before the pawn can queen. >> >>Is this correct? >> >>KarinsDad :) > >yes > >Uri It is not exactly correct because there are cases when the side with the knights can checkmate after the pawn queen and not before the pawn queen. Uri
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