User:^Vitiate^/sandbox

La equis (from the X) is a move in chess. It is a special knight that can only occur immediately after a player's king is put into check. A knight that has not previously moved may make an “L” shape of any size, extended from the usual 3 horizontal spaces in order to capture the piece threatening the king.

The La equis capture must be made on the very next turn or the right to do so is lost. Like any other move, if a la equis capture is the only legal move available, it must be played.

The la equis capture rule was added in the 17th century when castling was introduced. It prevents early victories and allows players to advance their front row without severe repercussion. The denial of an enemy effort to victory is where the name "the X" is derived from.

Conditions
The conditions to la equis are the following:


 * the capturing knight must have not been previously moved;
 * The captured piece must be putting the king in check;
 * the capture can only be made on the move immediately after the opposing piece puts the king in check