Author: Ricardo Gibert
Date: 04:59:08 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. I feel compelled to point out that White only just wins this thanks to the h-pawn: 1...c6 2.h4 a4 3.h5 b3 4.axb3 axb3 5.h6 b2 6.e7 Kf7 7.e8Q+ Kxe8 8.h7 b1Q 9.h8Q+ >> >>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. > >Uri
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