# 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.

The axiom is not a theorem of ZFC (assuming ZFC is consistent), but unlike the full axiom of determinacy (AD), which contradicts the axiom of choice, it is not known to be inconsistent with ZFC. 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.

## References[edit]

- Martin, Donald A.; Steel, John R. (Jan 1989). "A Proof of Projective Determinacy" (PDF).
*Journal of the American Mathematical Society*.**2**(1): 71–125. doi:10.2307/1990913. Archived from the original (PDF) on April 30, 2016. - Moschovakis, Yiannis N. (2009).
*Descriptive set theory*(PDF) (2nd ed.). Providence, R.I.: American Mathematical Society. ISBN 0-8218-4813-5. Archived from the original on 2014-11-12.CS1 maint: BOT: original-url status unknown (link)

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