 Since it is possible, for any formula_7, to construct a game in which player I has a winning strategy exactly when formula_7 contains a cone and in which player II has a winning strategy exactly when the complement of formula_7 contains a cone, the axiom of determinacy implies that the measure-1 sets of Turing degrees form an ultrafilter.It is easy to show that a countable intersection of cones is itself a cone; the Martin measure is therefore a countably complete filter.This fact, combined with the fact that the Martin measure may be transferred to formula_12 by a simple mapping, tells us that formula_12 is measurable under the axiom of determinacy.