English

Unbounded towers and products

General Topology 2019-12-06 v1

Abstract

We investigate products of sets of reals with combinatorial covering properties. A topological space satisfies S1(Γ,Γ)\mathsf{S}_1(\Gamma,\Gamma) if for each sequence of point-cofinite open covers of the space, one can pick one element from each cover and obtain a point-cofinite cover of the space. We prove that, if there is an unbounded tower, then there is a nontrivial set of reals satisfying S1(Γ,Γ)\mathsf{S}_1(\Gamma,\Gamma) in all finite powers. In contrast to earlier results, our proof does not require any additional set-theoretic assumptions. A topological space satisfies (ΩΓ)\Omega\choose\Gamma (also known as Gerlits--Nagy's property γ\gamma) if every open cover of the space such that each finite subset of the space is contained in a member of the cover, contains a point-cofinite cover of the space. We investigate products of sets satisfying (ΩΓ)\Omega\choose\Gamma and their relations to other classic combinatorial covering properties. We show that finite products of sets with a certain combinatorial structure satisfy (ΩΓ)\Omega\choose\Gamma and give necessary and sufficient conditions when these sets are productively (ΩΓ)\Omega\choose\Gamma.

Keywords

Cite

@article{arxiv.1912.02528,
  title  = {Unbounded towers and products},
  author = {Piotr Szewczak and Magdalena Włudecka},
  journal= {arXiv preprint arXiv:1912.02528},
  year   = {2019}
}

Comments

19 pages

R2 v1 2026-06-23T12:36:47.125Z