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Subject: Re: Counting & Encoding Any Chess Position in 157 bits

Author: Ratko V Tomic

Date: 00:30:24 11/15/99

Go up one level in this thread

```> 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.)

```