English

Relationships between computability-theoretic properties of problems

Logic 2019-03-12 v1

Abstract

A problem is a multivalued function from a set of \emph{instances} to a set of \emph{solutions}. We consider only instances and solutions coded by sets of integers. A problem admits preservation of some computability-theoretic weakness property if every computable instance of the problem admits a solution relative to which the property holds. For example, cone avoidance is the ability, given a non-computable set AA and a computable instance of a problem P\mathsf{P}, to find a solution relative to which AA is still non-computable. In this article, we compare relativized versions of computability-theoretic notions of preservation which have been studied in reverse mathematics, and prove that the ones which were not already separated by natural statements in the literature actually coincide. In particular, we prove that it is equivalent to admit avoidance of 1 cone, of ω\omega cones, of 1 hyperimmunity or of 1 non-Σ10\Sigma^0_1 definition. We also prove that the hierarchies of preservation of hyperimmunity and non-Σ10\Sigma^0_1 definitions coincide. On the other hand, none of these notions coincide in a non-relativized setting.

Keywords

Cite

@article{arxiv.1903.04273,
  title  = {Relationships between computability-theoretic properties of problems},
  author = {Rod Downey and Noam Greenberg and Matthew Harrison-Trainor and Ludovic Patey and Dan Turetsky},
  journal= {arXiv preprint arXiv:1903.04273},
  year   = {2019}
}

Comments

19 pages

R2 v1 2026-06-23T08:04:11.124Z