Alice chess

Move rules

At the start, pieces occupy their normal positions on board A, while board B is empty. On each turn, a player may move on either board A or B. Pieces move as in standard chess, but upon completing a move they transfer to the corresponding square on the opposite board. A move must be legal on the board where it is played, and the destination square on the opposite board must be vacant. Captures occur only on the board where the capturing piece currently stands; after capture, the piece transfers to the opposite board.

A player may be in check on the second board during a move on the first board if the transferred piece then blocks that check. The player must not be in check on the first board after the move but before the transfer, so the king cannot transfer out of check. After the transfer, the player must not be in check on either board, meaning they cannot create discovered check on the first board by transferring, and the king cannot transfer into check on the second board.

Castling is generally permitted, with both king and rook transferring to the second board. En passant capture is normally excluded but can be included; in most such games the target square is considered the square passed over on the first board, though opinions differ.

Early mates

Several early checkmates exist. One example: 1. e4 d5 2. Be2 dxe4 3. Bb5. Black cannot block the check by interposing a piece because any such piece disappears upon transferring to board B, and cannot escape via 3...Kd7 as that move is illegal on board A, resulting in checkmate. Another fool's mate: 1. e4 d6 2. Bc4 Qxd2?? 3. Bb5#. Additional examples include 1. e4 e5 2. Qh5 Nf6?? 3. Qxe5# and 1. d4 e6 2. Qd6 Be7? 3. Qe5+ Kf8 4. Bh6# (Seitz–Nadvorney, 1973).

Example game

A game from the 1996 AISE Grand Prix between Paul Yearout and George Jelliss, annotated by Jelliss, illustrates typical play. Moves returning to board A are notated /A. The game: 1. d3 Nf6 2. Nc3 c5 3. Qd2 Nc6 4. d4/A Rb8 5. e3 g5 6. f4 Rbg8/A 7. Nd5/A h6 8. Nf3 gxf4/A 9. Bxf4 Rg4 10. Be5/A Rh5 11. 0-0-0 11... Ne4/A 12. Bc7 Ra4/A 13. Ba6 Bg7 14. Bb5/A Rc4+ 15. Kb1/A Rf5/A 16. Ba5/A 16... Rxd5 17. Qxd5/A Qxa5 18. a3 Qd2/A 19. Qxd7+ Kf8 20. Qxg7/A Qc3 21. Rd8/A, and Black resigns.

Variations

Several rule modifications have produced variations of Alice chess. In one, the black army starts on board B. Null or zero moves are permitted, consisting only of transferring a piece to the corresponding vacant square on the opposite board; a king cannot escape check with a zero move, and castling is denied if either king or rook has made a zero move (John Ishkan, 1973). Another variation allows a move even if the square normally transferred to is occupied, omitting the transfer (Michael O'Donohue, 2003).

Jed Stone's 1981 variant has black starting on board B, transfers optional, non-pawn pieces may make zero moves and capture in so doing, a king is checked when an opposing piece sits on its zero square, and mate must cover the king's ability to flee via a zero move. Parton introduced an 8x4 version and noted that Alice chess can use three boards. The rules can be adopted by other chess variants by doubling the number of boards and applying the piece transfer policy.