English

Completely determined Borel sets and measurability

Logic 2021-05-20 v2

Abstract

We consider the reverse math strength of the statement C-DM\mathsf{C\text-DM}:"Every completely determined Borel set is measurable." Over WWKL0\mathsf{WWKL}_0, we obtain the following results analogous to the previously studied category case. C-DM\mathsf{C\text-DM} lies strictly between ATR0\mathsf{ATR}_0 and Lω1,ω-CA\mathsf{L}_{\omega_1,\omega}\text-\mathsf{CA}. Whenever M2ωM\subseteq 2^\omega is the second-order part of an ω\omega-model of C-DM\mathsf{C\text-DM}, then for every ZMZ \in M, there is a RMR \in M such that RR is Δ11\Delta^1_1-random relative to ZZ. On the other hand, without WWKL0\mathsf{WWKL}_0, all sets have measure zero (as measured according to C-DM\mathsf{C\text-DM}), and it follows vacuously that ¬WWKL0\neg \mathsf{WWKL}_0 implies C-DM\mathsf{C\text-DM} over RCA0\mathsf{RCA}_0.

Keywords

Cite

@article{arxiv.2001.01881,
  title  = {Completely determined Borel sets and measurability},
  author = {Linda Westrick},
  journal= {arXiv preprint arXiv:2001.01881},
  year   = {2021}
}

Comments

19 pages, minor revisions

R2 v1 2026-06-23T13:04:37.080Z