Axiom of projective determinacy

In mathematical logic, projective determinacy is the special case of the axiom of determinacy applying only to projective sets.

The axiom of projective determinacy, abbreviated PD, states that for any two-player infinite game of perfect information of length ω in which the players play natural numbers, if the victory set (for either player, since the projective sets are closed under complementation) is projective, then one player or the other has a winning strategy.