Π 0 1 ENCODABILITY AND OMNISCIENT REDUCTIONS

Abstract : A set of integers A is computably encodable if every infinite set of integers has an infinite subset computing A. By a result of Solovay, the computably encodable sets are exactly the hyperarithmetic ones. In this paper, we extend this notion of computable encodability to subsets of the Baire space and we characterize the Π01 encodable compact sets as those who admit a non-empty Σ11 subset. Thanks to this equivalence, we prove that weak weak König's lemma is not strongly computably reducible to Ramsey's theorem. This answers a question of Hirschfeldt and Jockusch.
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Benoit Monin, Ludovic Patey. Π 0 1 ENCODABILITY AND OMNISCIENT REDUCTIONS. Notre Dame Journal of Formal Logic, University of Notre Dame, 2016. ⟨hal-01397286⟩

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