English

On spaces with a $\pi$-base whose elements have an H-closed closure

General Topology 2024-02-12 v2

Abstract

We deal with the class of Hausdorff spaces having a π\pi-base whose elements have an H-closed closure. Carlson proved that X2wL(X)ψc(X)t(X)|X|\leq 2^{wL(X)\psi_c(X)t(X)} for every quasiregular space XX with a π\pi-base whose elements have an H-closed closure. We provide an example of a space XX having a π\pi-base whose elements have an H-closed closure which is not quasiregular (neither Urysohn) such that X>2wL(X)χ(X)|X|> 2^{wL(X)\chi(X)} (then X>2wL(X)ψc(X)t(X)|X|> 2^{wL(X)\psi_c(X)t(X)}). Still in the class of spaces with a π\pi-base whose elements have an H-closed closure, we establish the bound X2wL(X)k(X)|X|\leq2^{wL(X)k(X)} for Urysohn spaces and we give an example of an Urysohn space ZZ such that k(Z)<χ(Z)k(Z)<\chi(Z). Lastly, we present some equivalent conditions to the Martin's Axiom involving spaces with a π\pi-base whose elements have an H-closed closure and, additionally, we prove that if a quasiregular space has a π\pi-base whose elements have an H-closed closure then such space is Baire.

Cite

@article{arxiv.2401.17160,
  title  = {On spaces with a $\pi$-base whose elements have an H-closed closure},
  author = {Davide Giacopello},
  journal= {arXiv preprint arXiv:2401.17160},
  year   = {2024}
}
R2 v1 2026-06-28T14:32:03.565Z