H. G. Muller wrote on Tue, Nov 26, 2019 12:56 PM UTC:
This is a trial for using the Interactive Diagram for Alice Chess. Custom-supplied functions BadZone and WeirdPromotion take care of refusal of moves to squares of which the mirror square is occupied, and take care of shuttling the moved piece to the other board, respectively. The boards are separated by strip of 'hole' squares, which has to be two files wide to prevent Knights from crossing it.
I implemented e.p. capture as a move by the Pawn on the board where the doubly pushed Pawn started.
This seemed the least illogical way to do it, as the e.p. square on that board will always be empty (or the double push would not have been allowed).
And it is the square the double push really passed over, and thus where it could have been blocked.
The move could still be illegal because the corresponding square on the other board is occupied,
but that is normal for any move to an empty square in Alice Chess that would be legal on its own board.
There has to be no extra rule to prevent double capture this way.
This method of e.p. capture corresponds to one where the doubly pushed Pawn must first make a single retrograde step before being captured,
rather than replacing its double step by a single step.
That this is not the same is the fault of an Alice double push not really being two consecutive single pushes.
I still have a comment to make about the legality of moves (an aspect that the diagram doesn't address).
The ambiguity here seems to be caused by not making proper distinction between legal and pseudo-legal moves, but heaping them all under the term 'legal'.
A more precise description would have said that a move in Alice Chess is pseudo-legal if (before transfer) it would have been pseudo-legal in orthodox Chess on the board where it is made, and the target square on the other board is empty.
And then an Alice move is legal (as usual) when it does not expose the King to pseudo-legal Alice capture.
This prevents solving distant checks by interposing a piece that was on the board where the checked King resides (but then disappearing to the other board, so that the King can be captured) from being considered legal.
Despite the fact that they would have been perfectly legal orthodox Chess moves on the board with the King.
This is a trial for using the Interactive Diagram for Alice Chess. Custom-supplied functions BadZone and WeirdPromotion take care of refusal of moves to squares of which the mirror square is occupied, and take care of shuttling the moved piece to the other board, respectively. The boards are separated by strip of 'hole' squares, which has to be two files wide to prevent Knights from crossing it.
I implemented e.p. capture as a move by the Pawn on the board where the doubly pushed Pawn started. This seemed the least illogical way to do it, as the e.p. square on that board will always be empty (or the double push would not have been allowed). And it is the square the double push really passed over, and thus where it could have been blocked. The move could still be illegal because the corresponding square on the other board is occupied, but that is normal for any move to an empty square in Alice Chess that would be legal on its own board. There has to be no extra rule to prevent double capture this way. This method of e.p. capture corresponds to one where the doubly pushed Pawn must first make a single retrograde step before being captured, rather than replacing its double step by a single step. That this is not the same is the fault of an Alice double push not really being two consecutive single pushes.
I still have a comment to make about the legality of moves (an aspect that the diagram doesn't address). The ambiguity here seems to be caused by not making proper distinction between legal and pseudo-legal moves, but heaping them all under the term 'legal'. A more precise description would have said that a move in Alice Chess is pseudo-legal if (before transfer) it would have been pseudo-legal in orthodox Chess on the board where it is made, and the target square on the other board is empty. And then an Alice move is legal (as usual) when it does not expose the King to pseudo-legal Alice capture. This prevents solving distant checks by interposing a piece that was on the board where the checked King resides (but then disappearing to the other board, so that the King can be captured) from being considered legal. Despite the fact that they would have been perfectly legal orthodox Chess moves on the board with the King.