Universal co-analytic sets

Hjorth, Greg

doi:10.1090/S0002-9939-96-03494-6

Universal co-analytic sets
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by Greg Hjorth

Proc. Amer. Math. Soc. 124 (1996), 3867-3873

DOI: https://doi.org/10.1090/S0002-9939-96-03494-6

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Abstract:

There is a universal $\Pi _{1}^{1}$ equivalence relation. The existence of a $\Pi _{1}^{1}$ set universal for $\wideutilde {\Pi }_{1}^{1}$ non-Borel is independent of the usual axioms of mathematics.

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