Π₂¹ sets and Π₂¹ singletons

Harrington, Leo

doi:10.1090/S0002-9939-1975-0373896-5

$\Pi _{2}^{1}$ sets and $\Pi _{2}^{1}$ singletons
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Proc. Amer. Math. Soc. 52 (1975), 356-360 Request permission

Abstract:

The following are equivalent: (a) every real is constructible; (b) every nonempty $\prod _2^1$ set of reals contains a $\prod _2^1$ singleton. (Implication $({\text {a}}) \Rightarrow ({\text {b}})$ is due solely to H. Friedman.)

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