Benson's algorithm [3] can be used to determine which stones can never be captured even if the opponent would get many moves in a row. The algorithm is ran only for the current position and the result is used for three purposes: 1) The player never plays in an area that can be proven safe; 2) Blocks that are proven safe are no burden at all, when ants evaluate liberty changes (see Section 2.1); 3) There can be no vital points (see Section 2.2) in an area that is proven safe already. In practice, the game might end before any stones can be proven safe, so Benson's algorithm is not always very useful.