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General and Set-Theoretic Topology

General/ST Session Talk #4.1

Subevent of General/ST Session #4

HUMB 150

Times: 2025 Aug 13 from 08:30AM to 08:50AM (Central Time (US & Canada))

Webinar link: Icon: video Webinar

Cardinal bounds in spaces with a $\pi$-base whose elements have an H-closed closure

Davide Giacopello ⟨dagiacopello@unime.it⟩

Abstract:

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

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