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Subject: Re: Interesting endgame database probe problem

Author: blass uri

Date: 21:22:31 02/09/99

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On February 09, 1999 at 23:22:20, Robert Hyatt wrote:

>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...

I do not understand the problem of repetition.
I suppose you have a complete knowledge about KQP vs KQ
and if in the first position (KQP vs KQ) the tablbases showed mate in 60 then in
the next time it should be mate in 59 or mate in less moves.
The distance to mate is decreased every move so there cannot be repetition.

The only possible problem is the 50-move rule but this was not the problem in
this case.

Uri



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