In a nutshell: the capture of an enemy piece produces a piece belonging to both players. The game evolves in two phases (the second not always being reached).
* 'Undo' in this case means returning a checkered piece to the square from which it was moved during the preceding turn. If on the other hand the last move produced a new piece, a move that takes the piece to the square from which the capturing piece came is allowed.
Just as in regular chess, threefold repetition, fifty moves without moving a pawn or capturing a piece, as well as stalemate, lead to a draw. Checkered chess can produce some problematic, ambiguous stalemate situations as discussed below.
Again, as in regular chess, in order to win one must attack the opponent's king – if it could not escape being captured in the following move* it is in checkmate and the game is over.
Castling is permitted if the rook and the king have not yet moved. A checkered rook cannot be used to castle.
Castling is not permitted if the king is in check 'directly' (type 1) on its starting square or the adjacent square, and the king cannot be in either 'direct' or 'latent' check on the destination square.
Pawns move exactly as they do in regular chess with the addition of these subtle modalities:
A pawn captured on its starting square keeps the right to advance two squares. A checkered pawn that reaches the second or seventh row has no right to move two squares unless the original pawn from that square was never moved.
Checkered pawns cannot capture en passant as during the moment that the capture would be executed they belong to the other side. Otherwise, capture en passant remains legal.
Promotion takes place in the same way as in regular chess. If it happens through a capture the player can choose to create a checkered knight, bishop, rook or queen.
As originally conceived, the rules of Checkered Chess offer the possibility of the checkered pieces gaining their autonomy, under the control of either of the players or a third party.
Phase 1 - according to the rules above
Phase 2 - as described below
During the game a third person can decide to take control of the checkered pieces. They thus become autonomous and vulnerable to being captured - Phase 2. The game then proceeds with three turns, the checkered side taking a turn between the white and black sides according to their moment of entry into the game. Checkered pieces can now be captured and removed from play but the capture of a white or black piece by a white, black or checkered piece continues to produce a checkered piece. The checkered side can win by checkmating either of the kings.
If there is no third player, or before the third player has decided to adopt the checkered side, one of the two players can announce that they are taking control of the checkered side. The other player then finds themself in charge of both the white and black pieces, including the kings. The checkered side wins by checkmating either the white or black king, they lose if they are eliminated from play through capture of all checkered pieces.
NOTE: Only this latter variant is implemented on the web site.
During Phase 1 checkered pieces do not exert a threat on the king on its starting square or the squares that it passes through. In Phase 2 the line of attack of checkered pieces makes castling impossible - none of the squares on the king's trajectory can be under attack from a checkered piece.
In Phase 1 checkered pawns can move and capture only in the same direction as the pawns on the side to which they belong n that turn. In Phase 2 they can move and capture in either direction.
In Phase 1 capture en passant by a checkered piece is impossible. In Phase 2 it becomes legitimate.
As a checkered pawn can move in either direction during Phase 2 it can be promoted on either the first or eighth row. Promotion produces another checkered piece.
[Benjamin] Thanks to Bevis Martin for the english translation.
These rules are currently in the 'test' phase and may be modified as more games are played.
The rules of Checkered Chess were thought up by Patrick Bernier and developed with the help of Benjamin Auder.
Thanks also to Christian Poisson, Laurent Nouhaud and Frédéric Fradet.