English

Cousin's lemma in second-order arithmetic

Logic 2021-05-10 v1

Abstract

Cousin's lemma is a compactness principle that naturally arises when studying the gauge integral, a generalisation of the Lebesgue integral. We study the axiomatic strength of Cousin's lemma for various classes of functions, using Friedman and Simpson's reverse mathematics in second-order arithmetic. We prove that, over RCA0\mathsf{RCA}_0: (i) Cousin's lemma for continuous functions is equivalent to WKL0\mathsf{WKL}_0; (ii) Cousin's lemma for Baire class 1 functions is equivalent to ACA0\mathsf{ACA}_0; (iii) Cousin's lemma for Baire class 2 functions, or for Borel functions, are both equivalent to ATR0\mathsf{ATR}_0 (modulo some induction).

Cite

@article{arxiv.2105.02975,
  title  = {Cousin's lemma in second-order arithmetic},
  author = {Jordan Mitchell Barrett and Rodney G. Downey and Noam Greenberg},
  journal= {arXiv preprint arXiv:2105.02975},
  year   = {2021}
}

Comments

13 pages, no figures

R2 v1 2026-06-24T01:51:33.124Z