Castling Castling Castling is a move in the game of chess involving a player's king and either of the player's original rooks. It is the only move in chess in which a player moves two pieces in the same move, and it is the only move aside from the knight's move where a piece can be said to "jump over" another. Castling consists of moving the king two squares towards a rook on the player's first , then moving the rook to the square over which the king crossed. Castling may only be done if the king has never moved, the
Null-move heuristic of chess positions where employing the null-move heuristic can result in severe tactical blunders. In these "zugzwang" (German for "forced to move") positions, the player whose turn it is to move has only bad moves as their legal choices, and so would actually be better off if allowed to forfeit the right to move. In these positions, the null-move heuristic may produce a cutoff where a full search would not have found one, causing the program to assume the position is very good for a side when it may in fact be very bad for them. To avoid using the