English

Low$_2$ computably enumerable sets have hyperhypersimple supersets

Logic 2025-10-15 v3

Abstract

A longstanding question is to characterize the lattice of supersets (modulo finite sets), L(A)\mathcal{L}^*(A), of a low2_2 computably enumerable (c.e.) set. The conjecture is that L(A)E\mathcal{L}^*(A)\cong {\mathcal E}^*. In spite of claims in the literature, this longstanding question/conjecture remains open. We contribute to this problem by solving one of the main test cases. We show that if c.e.\ AA is low2_2 then AA has an atomless hyperhypersimple superset. In fact, if AA is c.e.\ and low2_2, then for any Σ3\Sigma_3-Boolean algebra~BB there is some c.e.\ HAH\supseteq A such that L(H)B\mathcal{L}^*(H)\cong B.

Keywords

Cite

@article{arxiv.2412.01939,
  title  = {Low$_2$ computably enumerable sets have hyperhypersimple supersets},
  author = {Peter Cholak and Rodney Downey and Noam Greenberg},
  journal= {arXiv preprint arXiv:2412.01939},
  year   = {2025}
}

Comments

Revised due to referee's comments. Thanks!

R2 v1 2026-06-28T20:20:27.154Z