 Subgame perfection can be used with extensive form games of complete but imperfect information.The subgame-perfect Nash equilibrium is normally deduced by "backward induction" from the various ultimate outcomes of the game, eliminating branches which would involve any player making a move that is not credible (because it is not optimal) from that node.One game in which the backward induction solution is well known is tic-tac-toe, but in theory even Go has such an optimum strategy for all players.