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# Shrink Chess

Pepijn van Erp send me the rules of the following chess variant. He found the rules in the periodical of STORM, the society for the faculty of Mathematics and Computer Science of the Free University in Amsterdam, and made some modifications to enhance playability to these rules.

## Rules

The game starts on a normal chessboard, with the usual opening setup. When a player moves a piece and thus doing so empties a row or column on the board, the board shrinks. This means that this empty row or column disappears from the board. In practice, this means that all pieces on one side of the line are moved one square in the direction of the line, and the last line (horizontal or vertical) now is no longer used. During the game, the board can only decrease in size - rows or columns never come back. It is easiest (for writing down the moves of the game, and remembering which lines are in play) to always shrink in the direction of a1.

A move may only be made when the position after the possible shrink is legal. For instance, it is not allowed to move such that your king is in check after the shrink due to your move.

• Long or short castling is only allowed when there are two or three squares between the king and the rook. For instance, when the d-column has disappeared, short castling on the queens side is allowed. (All usual requirements for castling also must be fulfilled.)
• A double first step with a pawn (like e2-e4) is only allowed when there are still 8 rows on the board.
• A player that causes a pawn to promote, decides which piece it is turned into. (This can possibly be the player not owning the pawn: e.g., when black has a pawn on a2, and white moves the only piece on the a-line to a square on another horizontal line, then the black pawn on a2 promotes: white can decide to which type of piece.)