Author: Robert Hyatt
Date: 20:10:50 07/15/03
Go up one level in this thread
On July 15, 2003 at 21:43:54, Omid David Tabibi wrote:
>On July 15, 2003 at 20:13:13, Robert Hyatt wrote:
>
>>On July 15, 2003 at 17:13:47, Andrea Griffini wrote:
>>
>>>A question about repeated positions... is the en-passant square
>>>part of the "position" even when no en-passant pawn capture is
>>>possible (because there is no capturing pawn, or because the
>>>theoretically capturing pawn is pinned on the file or because
>>>just the en-passant capture is "pinned") ?
>>
>>I don't believe so. At least not by the rules of FIDE. If a move is
>>illegal, it is not possible to play it. For EP, if the pawn can't
>>be taken because (a) it wasn't moved two squares, (b) no pawn is on
>>an adjacent file to take it; (c) a pawn is on the adjacent file but
>>can't legally make the capture due to being pinned; then the move
>>simply is not possible and a position with every piece on the same
>>square, where one was reached by two pawn pushes and the other by
>>one two-square pawn push, would be considered identical.
>>
>>>
>>>If this is not the case then checking for repeated positions
>>>gets way more annoying as my position hash code doesn't tell
>>>the whole story ... :(
>>
>>I don't hash the ep status if (a) the pawn didn't advance two squares;
>>(b) there is no pawn on either of the adjacent files that _can_ make a
>>pseudo-legal EP capture. I don't screen out the pinned business, however,
>>and haven't had it cause a problem.
>>
>
>I also do the hasing exactly like this, but thinking about it, a problem can
>arise:
>
>[D]3rk3/2p5/8/3P4/8/8/3K4/8 b - - 0 1
>Black(1): c7c5
>White(2): d2d3
>Black(2): d8d7
>White(3): d3d2
>Black(3): d7d8
>White(4): d2d3
>Black(4): d8d7
>White(5): d3d2
>Black(5): d7d8
>White(6): d2d3
>1/2-1/2 {Draw by threefold repetition}
>
>Actually in the above game it was already draw after black's 5th move Rd8, but
>since when black played c5 the ep square was wrongly set to c6, that position
>was considered different from the two arising later.
>
It's a bug, but I ignore it.
>>
>>>
>>>More concretely:
>>>
>>>8/8/8/8/1R4pk/8/5P2/5K2 w - - 0 1
>>>
>>>1. f4 Kh3 2. Ra4 Kh4 3. Rb4 Kh3 4. Ra4 Kh4 5. Rb4
>>>
>>>Is this "5. Rb4" drawing by third repetition of the position
>>>occured on the board after "1. f4" or not ?
>>>
>>>Andrea
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.