Author: Vincent Diepeveen
Date: 16:08:33 08/03/01
Go up one level in this thread
On August 03, 2001 at 15:44:09, Dieter Buerssner wrote:
>A small question about chess rules. Assume the following position (which does
>not make any other sense, than to show my point):
>
>[D] 3kr3/8/8/8/3p4/8/4P3/3RK3 w - - 0 1
>
>1. e4
>
>Now black cannot capture ep. Then just some stupid moves:
>
>1...Kd7 2. Ke2 Kd8 3. Ke1
>
>Again the same postion as after 1. e4.
>
>3...Kd7 4. Ke2 Kd8
>Can at this point White claim a draw, by saying "I intend to move Ke1 - 3fold
>repetion"?
to claim a draw you need 3 times the same position p.
1.e4 now we have position p black to move #1
1..kd7 2.ke2 kd8 3.ke1 now we have position p black to move #2
3...kd7 4.ke2 kd8 4.Ke1 now only after making the move we have p #3 times.
In all the 3 positions there is
a) no possibility to capture en passant
b) castling status didn't change
c) the same position occured on the board (logically no pawn moves
or captures were made otherwise you don't have thesame board position)
So you can claim the draw.
>I assume yes. If this is correct: Are you handling this correctly in your
>chess-engine?
No i am not.
I would be amazed if anyone is, because what you need would
be only hashing en passant if en passant is legal in that position.
That's requiring quite a bit of system time extra.
>The reason why I ask. For the position after 1. e4 the engine may set the
>ep-square. I am doing this for Yace. It would be rather expensive, to check, if
>the actual ep capture is legal (at least, it would be expensive doing this in
>the search). At a later point, Yace will of course recognize, that the
>ep-capture is not legal, but then it is too late ...
>
>And a related question about Nalimov EGTBs. I have learned, that setting the ep
>square for the TB-probing in positions, where no ep capture is possible, returns
>invalid results. I recognized this in KNPKN. I earlier just set the ep-square
>after any double pawn push. This had now influence on the search/move-generation
>logic of my program. But probing of the TB with the ep-square set yielded wrong
>results. I fixed this.
>
>Now, I wonder, if the TBs will work correctly in the above scenario, when it
>really looks like the ep capture is possible at first sight, but it is not
>allowed, because the pawn is pinned.
>
>I think, the only available TBs, for this to occure are KXPKP for X=B,R,Q. I
>have neither of those, so I can't check.
>
>Regards,
>Dieter
I bet for game relevant positions it didn't change a bit though.
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