English

Topological spaces with an $\omega^\omega$-base

General Topology 2021-11-01 v9 Logic

Abstract

Given a partially ordered set PP we study properties of topological spaces XX admitting a PP-base, i.e., an indexed family (Uα)αP(U_\alpha)_{\alpha\in P} of subsets of X×XX\times X such that UβUαU_\beta\subset U_\alpha for all αβ\alpha\le\beta in PP and for every xXx\in X the family (Uα[x])αP(U_\alpha[x])_{\alpha\in P} of balls Uα[x]={yX:(x,y)Uα}U_\alpha[x]=\{y\in X:(x,y)\in U_\alpha\} is a neighborhood base at xx. A PP-base (Uα)αP(U_\alpha)_{\alpha\in P} for XX is called locally uniform if the family of entourages (UαUα1Uα)αP(U_\alpha U_\alpha^{-1}U_\alpha)_{\alpha\in P} remains a PP-base for XX. A topological space is first-countable if and only if it has an ω\omega-base. By Moore's Metrization Theorem, a topological space is metrizable if and only if it is a T0T_0-space with a locally uniform ω\omega-base. In the paper we shall study topological spaces possessing a (locally uniform) ωω\omega^\omega-base. Our results show that spaces with an ωω\omega^\omega-base share some common properties with first countable spaces, in particular, many known upper bounds on the cardinality of first-countable spaces remain true for countably tight ωω\omega^\omega-based topological spaces. On the other hand, topological spaces with a locally uniform ωω\omega^\omega-base have many properties, typical for generalized metric spaces. Also we study Tychonoff spaces whose universal (pre- or quasi-) uniformity has an ωω\omega^\omega-base and show that such spaces are close to being σ\sigma-compact.

Keywords

Cite

@article{arxiv.1607.07978,
  title  = {Topological spaces with an $\omega^\omega$-base},
  author = {Taras Banakh},
  journal= {arXiv preprint arXiv:1607.07978},
  year   = {2021}
}

Comments

105 pages

R2 v1 2026-06-22T15:05:20.109Z