English

Analytic equivalence relations satisfying hyperarithmetic-is-recursive

Logic 2013-06-12 v2

Abstract

We prove, in ZF+Σ21\bf\Sigma^1_2-determinacy, that for any analytic equivalence relation EE, the following three statements are equivalent: (1) EE does not have perfectly many classes, (2) EE satisfies hyperarithmetic-is-recursive on a cone, and (3) relative to some oracle, for every equivalence class [Y]E[Y]_E we have that a real XX computes a member of the equivalence class if and only if \om1X\om1[Y]\om_1^X\geq\om_1^{[Y]}. We also show that the implication from (1) to (2) is equivalent to the existence of sharps over ZFZF.

Keywords

Cite

@article{arxiv.1306.1513,
  title  = {Analytic equivalence relations satisfying hyperarithmetic-is-recursive},
  author = {Antonio Montalbán},
  journal= {arXiv preprint arXiv:1306.1513},
  year   = {2013}
}
R2 v1 2026-06-22T00:29:25.018Z