Unbounded towers and products

Autor: Piotr Szewczak, Magdalena Włudecka
Rok vydání: 2021
Předmět:
Zdroj: Annals of Pure and Applied Logic. 172:102900
ISSN: 0168-0072
DOI: 10.1016/j.apal.2020.102900
Popis: We investigate products of sets of reals with combinatorial covering properties. A topological space satisfies $\mathsf{S}_1(\Gamma,\Gamma)$ 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 $\mathsf{S}_1(\Gamma,\Gamma)$ in all finite powers. In contrast to earlier results, our proof does not require any additional set-theoretic assumptions. A topological space satisfies $\Omega\choose\Gamma$ (also known as Gerlits--Nagy's property $\gamma$) 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 $\Omega\choose\Gamma$ and their relations to other classic combinatorial covering properties. We show that finite products of sets with a certain combinatorial structure satisfy $\Omega\choose\Gamma$ and give necessary and sufficient conditions when these sets are productively $\Omega\choose\Gamma$.
Comment: 19 pages
Databáze: OpenAIRE
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