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Subject: Re: Interesting endgame database probe problem

Author: Robert Hyatt

Date: 20:22:20 02/09/99

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On February 09, 1999 at 04:17:18, blass uri wrote:

>
>On February 08, 1999 at 16:25:33, Robert Hyatt wrote:
>
>>On February 08, 1999 at 11:18:50, José de Jesús García Ruvalcaba wrote:
>>
>>>On February 07, 1999 at 18:30:17, Robert Hyatt wrote:
>>>
>
>>>	I see that crafty would never give up the h-pawn to reach a drawn QP vs Q
>>>ending. So I assume that the position after 96. Qxh5+ is won for black.
>>>	I do not understand why, in a tablebase position, crafty allowed the same
>>>position to appear twice (however, I understand why it allowed the third
>>>repetition now). If crafty is in a won tablebase position, the distance to mate
>>>should decrease every move.
>>>
>>
>>that was the 'bug' I reported.  in my search, I tried all moves at ply=1,
>>but at ply=2 did the tablebase probe _before_ trying any opponent moves.  And
>>since I did this, I made a move that led to the shortest possible mate, but
>>also led to a position where when the opponent moved, it repeated the position
>>for the third time.
>
>I did not understand it.
>If you are in a won position then it is enough to look only at all moves at
>ply=1 and to choose the best move(shortest distance to mate).
>
>If the distance to mate is decreased every move then repetition is impossible
>because repetition of distance to mate is impossible.
>
>Uri


this is wrong.. the problem is that a DTM database says 'n moves to mate from
this position' without knowing what has happened already in the game.  So it is
quite easy to follow a path to the shortest mate and stumble over a position
that leads to a draw.  the 50-move rule is the classic, because there are _lots_
of mates in > 50 with no pawn moves or captures before the mate is delivered.

In my case, it was just a problem of probing the table _before_ checking for
a repetition...



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