Axiom of projective determinacy
- 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 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.
The axiom is undecidable in ZFC, unlike the full axiom of determinacy (AD), which contradicts the Axiom of Choice. PD follows from certain large cardinal axioms, such as the existence of infinitely many Woodin cardinals.
PD implies that all projective sets are Lebesgue measurable (in fact, universally measurable) and have the perfect set property and the property of Baire. It also implies that every projective binary relation may be uniformized by a projective set.
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