English

Countably perfectly meager sets

Logic 2021-06-08 v3 General Topology

Abstract

We study a strengthening of the notion of a perfectly meager set. We say that that a subset AA of a perfect Polish space XX is countably perfectly meager in XX, if for every sequence of perfect subsets {Pn:nN}\{P_n: n \in {\mathbb N}\} of XX, there exists an FσF_\sigma-set FF in XX such that AFA \subseteq F and FPnF\cap P_n is meager in PnP_n for each nn. We give various characterizations and examples of countably perfectly meager sets. We prove that not every universally meager set is countably perfectly meager correcting an earlier result of Bartoszy\'nski.

Keywords

Cite

@article{arxiv.2010.08812,
  title  = {Countably perfectly meager sets},
  author = {Roman Pol and Piotr Zakrzewski},
  journal= {arXiv preprint arXiv:2010.08812},
  year   = {2021}
}

Comments

16 pages

R2 v1 2026-06-23T19:25:19.570Z