Author: Gerrit Reubold
Date: 01:16:50 01/24/01
Go up one level in this thread
On January 24, 2001 at 01:19:45, Uri Blass wrote: >On January 24, 2001 at 00:24:23, Robert Hyatt wrote: > >>On January 23, 2001 at 13:45:24, Gerrit Reubold wrote: >> >>>On January 22, 2001 at 16:02:56, Robert Hyatt wrote: >>> >>><big snip> >>> >>>>The problem is endgame knowledge. A program _ought_ to know that if you have >>>>a passer, then trade pieces to reach a won ending. Only in this case, that >>>>heuristic back-fires as it is black who ends up winning. This is a _tough_ >>>>exception to handle... >>>> >>>>although a GM would tell you instantly "No I won't trade queens..." >>> >>>Hello all, >>> >>>I think stating that a GM would know instantly that trading queens lose is >>>misguiding. One tempo decides whether the queen exchange loses or wins. Both a >>>GM and a chess engine should calculate here and not simply trust their >>>evaluation. Of course, "tell you instantly" could mean that the GM did the >>>calculations unconsciuosly and super-fast, but I don't think it was meant this >>>way. >>> >> >> >>I calculated it like this: >> >>1. remove queens. it is now white's move. Can white force those connected >>passers in? not quickly. > >You need to calculate to find that not quickly enough. > >look at this position when the king is in h2 and not in h1: > >[D]6k1/2p5/4P3/p3PP2/1p1P4/7P/P6K/8 b - - 0 1 > >In this case white can force the connected pawns quickly enough because the >passed pawns queens with check. >> >>2. what about black's b-pawn? Can white stop it? no. >> >>moral: don't trade queens _yet_. >> >>Crafty understands how to 'count squares' to see if a pawn can be caught or >>not. It just doesn't yet know how to apply that to 'candidate passers' since >>it costs a couple of tempi to make the passer, then more to run it in. >> >> >> >>>Consider the following changes to the position after blacks 45.th move: >>> >>>(a) if the black a-pawn were on a6 instead of a5: 46. Qe6+ wins, but it is not >>>obvious. >>>(b) if the white King were on g2 instead on h1: 46. Qe6+ wins, even less >>>obvious. >> >>these are easy (obvious) to me. just ask "can the king reach the queening >>square of the b pawn or not?" > > >The king cannot reach the b pawn from g2 but white wins because black does not >force a new queen with check and can do it only without check so white can >promote one of the passed pawn to be a new queen and we get again a queen >endgame. > >I think that programs should see that black has unstoppable passed pawn but >should also see that white has unstoppable passed pawn and the only way to know >which pawn is winning is by caculating. That was my point. The king on g2 is still unable to reach the b-pawn, but the position is nevertheless won for white. This is the problem with the obvious things in chess, we may lose games because of them (i.e. because of our lazyness, too lazy to calculate). BTW, I think it is possible that the GM would make the same mistake and misevaluate the queen exchange in Uri's position (white king at h2). Of course the GM is able to calculate it correctly, but the danger is that he doesn't calculate at all. > >Uri
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