Author: Dann Corbit
Date: 10:53:01 07/12/01
Go up one level in this thread
On July 11, 2001 at 19:49:45, Miguel A. Ballicora wrote: >On July 11, 2001 at 19:12:47, Dann Corbit wrote: > >>On July 11, 2001 at 19:02:24, Bruce Moreland wrote: >> >>>On July 11, 2001 at 18:55:45, Dann Corbit wrote: >>> >>>>>As a consequence the FEN generated from such positions is not strictly >>>>>correct according to the standard from SJE, but IMO the standard should >>>>>be changed, here. > >They are still correct IMHO. See below. > >>>> >>>>Yes, I think the current PGN standard is broken in regard to e.p. squares. > >I do not think is is broken, I think it is just ugly. I believe it has been >thought to allow certain programs to spit FENs in a faster/lazier way. >My interpretation is that the spirit is "one FEN determines a position, but a >position could be determined by different FENs" >After all, nobody will compare FEN databases in text mode to find duplicates... >or at least I guess that it was the idea. > >be >>>> >>>>For instance, how many distinct positions is this: >>>>[D]rnbqkbnr/ppp1pppp/8/3p4/3P4/8/PPP1PPPP/RNBQKBNR w KQkq - >>>>You can make 4 of them, if you have to set e.p. flags, but there is only one >>>>real position. Multiply the number of potential pawns affected and it explodes >>>>with great stupidity. >>> >>>Wait a sec. Does the FEN standard according to SJE state that you *have* to >>>have the ep square set to e3 after 1. e4? If so, that is dumb and I'm going to >>>happily ignore it. The square shouldn't be set unless there is a legal capture, >>>or at least it should be optional to set it if there isn't. >> >>"16.1.3.4: En passant target square >> >>The fourth field is the en passant target square. If there is no en passant >>target square then the single character symbol "-" appears. If there is an en >>passant target square then is represented by a lowercase file character >>immediately followed by a rank digit. Obviously, the rank digit will be "3" >>following a white pawn double advance (Black is the active color) or else be >>the digit "6" after a black pawn double advance (White being the active color). >> >>An en passant target square is given if and only if the last move was a pawn >>advance of two squares. Therefore, an en passant target square field may have > ^^^^^^^^ >>a square name even if there is no pawn of the opposing side that may >>immediately execute the en passant capture." > >Notice that it says "may have" rather than "must have". However, the previous sentence says "if and only if" and therefore it is required at all times. If a capture can be made, then there is an opposing side pawn. If a capture cannot be made there is none. I also verified the meaning with Steven J. Edwards. At any rate, I have asked him to change the meaning for the next iteration of the standard.
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