Touch-move rule move or capture the first of the pieces that they touched. If it cannot be determined whether he touched his own piece or the opponent's piece first, it is assumed that he touched his own piece first. If a player touches more than one piece, he must move or capture the first piece that can be legally moved or captured. An exception to that is an attempted illegal castling; in that case the king must be moved if possible, but otherwise there is no requirement to move the rook. When castling, the king must be the first piece touched. If
Null-move heuristic to guess cutoffs with less effort than would otherwise be required, whilst retaining a reasonable level of accuracy. The null-move heuristic is based on the fact that most reasonable chess moves improve the position for the side that played them. So, if the player whose turn it is to move can forfeit the right to move (or make a null move - an illegal action in chess) and still have a position strong enough to produce a cutoff, then the current position would almost certainly produce a cutoff if the current player actually moved. In employing the null-move heuristic, the