Alice chess

Alice chess, created by V. R. Parton in 1953, uses two ordinary boards, called A and B, but only one set of pieces. In the basic form, every piece starts on its normal square on board A and board B begins empty. A physical piece exists on only one board at a time.

How a move is completed

1. Choose a piece on its current board and make a move that is legal there under that piece's normal movement.
2. Check the square with the same coordinates on the other board. It must be empty.
3. After the move or capture, transfer the moving piece to that corresponding square on the other board.

A capture takes place on the departure board. The captured piece is removed, and the capturing piece then crosses to the other board. A piece on board A does not block a rook, bishop, or queen moving on board B because the boards are separate spaces.

The second condition creates many surprising restrictions. A destination may look empty on the departure board, yet the move is illegal if the corresponding arrival square is occupied. A defensive move can also fail because an interposing piece vanishes from that board when its transfer is completed.

The objective remains checkmate, meaning an attack on the king with no legal reply. Attacks and escapes must still obey the transfer rule. A king cannot flee to a square whose counterpart on the other board is occupied. Castling, the joint king-and-rook move, is commonly allowed with both pieces transferred, while secondary rules such as en passant, a special pawn capture following an opposing two-square advance, may differ between implementations.