English

Pi01 encodability and omniscient reductions

Logic 2019-09-18 v2

Abstract

A set of integers AA is computably encodable if every infinite set of integers has an infinite subset computing AA. 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 Π10\Pi^0_1 encodable compact sets as those who admit a non-empty Σ11\Sigma^1_1 subset. Thanks to this equivalence, we prove that weak weak K\"onig's lemma is not strongly computably reducible to Ramsey's theorem. This answers a question of Hirschfeldt and Jockusch.

Keywords

Cite

@article{arxiv.1603.01086,
  title  = {Pi01 encodability and omniscient reductions},
  author = {Benoit Monin and Ludovic Patey},
  journal= {arXiv preprint arXiv:1603.01086},
  year   = {2019}
}

Comments

9 pages

R2 v1 2026-06-22T13:03:02.523Z