Author: Uri Blass
Date: 21:23:28 07/15/03
Go up one level in this thread
On July 16, 2003 at 00:14:38, Omid David Tabibi wrote: >On July 15, 2003 at 22:35:20, Uri Blass wrote: > >>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: >> >>1)I think that even if the price of fixing it is only being 0.01% slower then it >>is still better not to fix it if you care about playing strength. >> >>2)Movei knows about pins but I cannot decide that a pinned pawn cannot do the en >>passent capture because the pawn can be pinned by a bishop and in part of these >>cases it can do the enpassent capture. >> >>Another point is that there are cases when enpassent capture is illegal inspite >>of the fact that the pawn is not pinned because there is an enemy rook or enemy >>queen in the same rank of the king. >> > >This discussion remined me of an old puzzle: can you setup a position in which a >king is simultaneously checked by two queens?! > >(answer down the page) Another question: Can you setup a position when the king is simultaneously checked from 2 rooks directions? (Answer down the page) promotion is enough. White Rook(Queen) a6, pawn a7. Black King a8 rook b8. axb8=rook(Queen) make the check from 2 rook directions. I made in the early stage of movei the false assumption that king can not be checked from 2 rook direction and I also reported the mistake here. Fortunately it cannot be checked from 2 diagnols. Uri
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