Reversion

Reversion is a move or sequence of moves that returns the board to a position that occurred earlier in the game. Positions are compared with earlier positions, usually after captures or during cyclical play.

Basic ko prevents an immediate local reversion, while superko rules can prohibit broader repetitions. The purpose is to identify and regulate repeated positions that could otherwise permit endless cycles.

Reversion differs from transposition: reversion means returning to an earlier position, whereas transposition means reaching the same position through different move orders and does not necessarily mean that the position is being repeated in play. Its exact scope and legality depend on the ruleset, including whether it uses simple ko, positional superko, or situational superko.