Author: Ricardo Gibert
Date: 08:49:55 01/24/01
Go up one level in this thread
On January 24, 2001 at 10:38:28, Robert Hyatt wrote: >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 > >OK. Black is going to get a queen in 4 moves. a4, b3, b2 and b1, or >a4, b3, bxa2 a1, or if white wastes one tempo, a4, b3 axb3 b2 and b1. IE >if white ignores it, 4 moves, if white wastes one move, it takes 5, but that >is still 4 moves effectively. > >Now for black. > >Here I don't see any way for white to make a queen in 4 moves, or to make >moves that force black to move his king and delay his queening plan. What am >I overlooking? d4-d5-d6-d7-d8 makes 4 effective moves for White. I set the position up with white having the three pawns and >king exactly as in your position, but black having a pawn on b5, which leaves >it with the same number of moves. Crafty can't find a way for white to win >this... > > > > >> >>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. >> >>Uri
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