English

Computable Ramsey's Theorem for Pairs Needs Infinitely Many Pi-0-2 Sets

Logic 2015-07-14 v1

Abstract

In \cite{J}, Theorem 4.2, Jockusch proves that for any computable k-coloring of pairs of integers, there is an infinite Π20\Pi^0_2 homogeneous set. The proof uses a countable collection of Π20\Pi^0_2 sets as potential infinite homogeneous sets. In a remark preceding the proof, Jockusch states without proof that it can be shown that there is no computable way to prove this result with a finite number of Π20\Pi^0_2 sets. We provide a proof of this latter fact.

Keywords

Cite

@article{arxiv.1507.03256,
  title  = {Computable Ramsey's Theorem for Pairs Needs Infinitely Many Pi-0-2 Sets},
  author = {Gregory Igusa and Henry Towsner},
  journal= {arXiv preprint arXiv:1507.03256},
  year   = {2015}
}
R2 v1 2026-06-22T10:10:20.937Z