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Levi Aho wrote on 2010-02-10 UTC

En Passant

While reading through the various discussions on en passant in Alice Chess, I came up with an option not mentioned that seems to be quite consistant with the core rules: When making an en passant capture, it's irellevant if the destination square on the board of the capturing piece is occupied, as the pawn really ends up on the other board, which is open.

This satisfies the three main rules:

1. A move must be legal on the board where it is played: By standard Chess rules an en passant capture is allowed when a double pawn move places a pawn adjacent to an enemy pawn.
2. A piece can only move or capture if the corresponding destination square on the other board is vacant: In order for the captured pawn to have made a double move, this must be true.
3. After moving, the piece is transfered to the corresponding square on the other board: This applies as normal.

This interpretation may seem strange, but it's entirely internally consistant. The standard chess en passant rules have no provisio for the destination square being occupied because it's impossible. I propose Alice Chess ought to have none, because it's irrellevant (unlike other variants where this issue is raised).

The other interpretation (that the destination square must be empty) really only makes sense if paired with a rule that makes double pawn moves illegal is such cases. In which case, the supposed ambiguity is, once again, not possible. However, I don't really like this option.

Firstly, it adds additional complications to the rules. With all other moves, legality is determined by the state of board the piece starts on. However, the legality of double pawn moves is dependant on both boards.

Secondly, the basis of this rule is that a double pawn move basically two seperate moves. If that was the case, in Alice Chess the pawn would end back on the board it started on. (Which could be an interesting option. If you handle en passant as I suggest, it works.)

Check

While there seems to be no special mention of check and mate in the rules on this page, it seems to me that it ought to be handled as normal. In other words, the king is in check if it could be captured on the next move.

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