Author: Ratko V Tomic
Date: 00:30:24 11/15/99
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> Two questions: > > 1) I didn't see side to move here. Another bit? I assume white is to move (as in the chess problems). This doesn't really lose anything "chesswise" since for every position with white to move there is a twin position with reversed colors also with white to move, therefore equivalent to the first position in which black had the turn. Overall I think that it doesn't make much sense mixing these types of issues (ep, castle, side to move, 3-repetition, 50-move, etc) with the combinatorics of the chess positions. Namely, even if you know the ep, castle and the side to move, you still can't continue to play a legal game from that position, unless you also know all the positions since the last capture or a pawn move (whichever came last), since you don't know how many times each of the positions you may get into occured earlier, and how many moves till the 50-move rule kicks in. You would need a position as far as 99 plies back, plus up to 99 plies leading to the current position to _really_ be able to play the legal game from that point on. Since, to paraphrase Kronecker, the laws of combinatorics come from God and the 50-move rule, 3-repetition rules, etc come from humans, they're apples and oranges. One might as well ask to encode also the clock settings for each side, the type of time and various game limits and so on, since any of those might be considered necessary in some contexts to play the fully legal game from the given position on. > 2) How do you decode such a monster? To paraphrase yet another mathematician, this can be done quite elegantly, but the answer is a bit too long to fit on this margin. (Well, there are few thoughts on this question in the followup post.)
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