Nitpicky question regarding 3-fold repetition

[frankp]

You can be sure it doesn't. The purpose of XBoard is to be useful, not to follow FIDE rules, which are obviously made for humans, and counter-productive or pointless when appled to computers. If you want to play by FIDE rules, invite a FIDE arbiter, and buy a Chess board and clock...

? wow

[gschmidt]

The rule is simple.

It is. I think some confusion resulted on my part after reading a description which seemed to imply that the position had to be the result of a move from the same player (not true), hence putting the initial position in question. Defining it in terms of moves available rather than "player who moved" make the rule perfectly clear.

[mhalstern]

What if for 2 of the repetitions, one of the white knights was on E7 and the other on F2. For the 3rd repetition, there were white knights on E7 and F2, however, the were not the same knights?

[hgm]

Like electrons in physces, Knights are indistinguishable in Chess. So the positions count as the same.

[Sven]

Defining it in terms of moves available rather than "player who moved" make the rule perfectly clear.

As already pointed out, it is not only about "moves available" but also about availability of castling rights. For instance in standard chess, consider Position A where White has kingside castling right (both king and rook have not moved yet) but there is a piece between king and rook which currently prevents White from actually castling, so the kingside castle is not part of the "available moves". Now in position B, everything is identical to A except that White has already moved the rook H1 (and moved back to H1), so the kingside castling right is lost. A and B are different, so B is no repetition of A, although "available moves" are identical at the moment if you define "available moves" as the set of moves that are legal in a position. In both A and B, kingside castling is not legal but in A the castling right is available for the future.

What you compare in fact to determine identity of positions are
1) location of pieces,
2) side to move,
3) castling rights,
4) en passant target square.

Sven

[hgm]

A nice illustration from everyday practice:

Code: Select all

[Event "Computer Chess Game"]
[Site "SCHAAK_PC"]
[Date "2010.04.07"]
[Round "1.5"]
[White "New Engine 0.16"]
[Black "Horizon 4.3"]
[Result "1-0"]
[TimeControl "40/60"]
[Number "196"]

1. d4 Nf6 2. c4 e6 3. Nf3 Bb4+ 4. Bd2 Qe7 5. g3 Nc6 6. Bg2 Bxd2+ 7. Nbxd2
d6 8. O-O O-O 9. e4 e5 10. d5 Nb8 11. Qb3 Na6 12. Qa4 Bd7 13. Qa3 c5 14.
Qb3 Rab8 15. Qa3 Ra8 16. Qb3 Rab8 17. Qa3 Ra8
{False draw claim: 'Draw by Repetition (Horizon)'} 1-0

[gschmidt]

As already pointed out, it is not only about "moves available" but also about availability of castling rights.

That's correct of course, I should have been more precise. What I meant was that "moves available" is a good way to think about it but it only gets you 90% there.

[LiquidNitrogenOverclocker]

If the other side is to move, the positions are indeed not the same. For the initial position of standard Chess this cannot happen, b.t.w. There is no possible sequence of moves that would recreate the position with the other side to move

I don't think that is true. Take a simple case.

1. e4 e5

It is now white to move.

1. e3 e5 2. e4

It is now black to move.

[hgm]

We were talking about the initial position. In standard Chess it always requires an even number of moves by each side to return to that, because the only reversible moves are with Knights, which always change color, and after they moved out, by the Rooks. But the Rooks also only have room for moves that change the color they are on.

In Gothic Chess this would be different: You can move out a Chancellor, Cd3 - Cf3 - Ce1, and it would be back in an odd number of moves.