Alcaxar rules
Version 1.1
(February 22, 2014)
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Players: two; they are referred to as "Red" and "Green".
Gameboard: 16 squares arranged in a four-by-four grid; at each square’s corner a tower serves as support for the walls acting as partitions between the squares.
Pieces: one Red Knight, one Green Knight, eight walls that do not belong to anybody and therefore can be moved by either player.
Objective of the game: either trapping the opponent’s knight or conquering the opponent’s fortress.

How to play
The figure shows the initial position of the pieces.
The squares in which the knights are placed are their fortresses.
Each player owns and moves the knight of his color.
The Red player moves first by convention, then players alternate.
A game turn is accomplished by one Red move and one Green move.
Players may not pass: on his turn, a player must move either his knight or a wall.

Knight’s movement
Knights move one square at a time horizontally or vertically, provided that the way is clear: a knight may not leap over a wall nor occupy the other knight’s square.

Wall’s movement
A wall moves as it were a door fixed to one of its two side-towers, therefore the wall’s movement consists in a clockwise or counterclockwise rotation around a tower.
The rotation may be one, two or three right angles wide.

The way must be clear: a wall may not rotate leaping over another wall nor over a knight.

A wall may rotate outside the board, but at the end of the movement it must be placed between two towers again.

Immediately after a player has moved a wall, the opponent may not reply moving the same wall, nor he may move those walls that are supported by the two towers the wall has joined at the end of its rotation.

A player may not play any wall's move that causes the entrapment of his own knight.

End of the game
A player can win in different ways.

1 - Trapping the opponent’s knight
This case occurs when a player has moved a wall or his knight so that the opponent’s knight can no longer reach any of the adjacent squares.

2 - Conquering the opponent’s fortress
This case occurs when a player moves his knight and it reaches the opponent’s fortress.

3 - Gaining a favourable stalemate
The game is over if the position that a move originates has previously occurred twice (stalemate by threefold repetition of a position: the initial position is relevant and must be taken into account, whereas it is not relevant whether walls are blocked).
The following criteria have to be considered in order to declare the winner of the stalemate:
a) distance between the knight and the opponent’s fortress (measured in squares along the shortest path, ignoring the other pieces);
b) number of adjacent squares the knight can move to.
The player who boasts the shortest distance (criterion a) wins; in case of a tie, the player who boasts more accessible squares (criterion b) wins. In case of a further tie, the Green player wins. A stalemate may never result in a draw.

If the game is played with time control, a player wins when the opponent runs out of time.

Alcaxar games and positions are recorded using an algebraic notation.
In order to permit the position of the walls to be recorded, the board must be considered as it were composed of nine rows (denoted with numbers 1 to 9) and nine columns (denoted with letters a to i), thus including not only the ranks and files of squares but also those of towers.

The initial position can be written as:
Red Knight: b8
Green Knight: h2
Walls: b5, c6, d7, e8, e2, f3, g4, h5

Knight’s moves are recorded using the letter K followed by the destination square, because this notation is always unambiguous, whereas wall’s moves have to be recorded putting the position from which the wall moved (in place of a piece initial) before the destination.
Alcaxar moves can be annotated with punctuation marks and other symbols:
   - a move that places the opponent under the threat of losing the game on the very next turn has the notation "+" added;
   - a move that enables the player to win the game (stalemate excluded) has the notation "≠" added;
   - a move that leads to a stalemate has the notation "≡" added;
   - "!" indicates a good move;
   - "?" indicates a mistake