English

On iso-dense and scattered spaces in $\mathbf{ZF}$

General Topology 2021-01-11 v1

Abstract

A topological space is iso-dense if it has a dense set of isolated points. A topological space is scattered if each of its non-empty subspaces has an isolated point. In ZF\mathbf{ZF}, in the absence of the axiom of choice, basic properties of iso-dense spaces are investigated. A new permutation model is constructed in which a discrete weakly Dedekind-finite space can have the Cantor set as a remainder. A metrization theorem for a class of quasi-metric spaces is deduced. The statement "every compact scattered metrizable space is separable" and several other statements about metric iso-dense spaces are shown to be equivalent to the countable axiom of choice for families of finite sets. Results concerning the problem of whether it is provable in ZF\mathbf{ZF} that every non-discrete compact metrizable space contains an infinite compact scattered subspace are also included.

Keywords

Cite

@article{arxiv.2101.02825,
  title  = {On iso-dense and scattered spaces in $\mathbf{ZF}$},
  author = {Kyriakos Keremedis and Eleftherios Tachtsis and Eliza Wajch},
  journal= {arXiv preprint arXiv:2101.02825},
  year   = {2021}
}

Comments

arXiv admin note: text overlap with arXiv:2009.09526

R2 v1 2026-06-23T21:54:12.366Z