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

Giacopello, D. (2024). On spaces with a $$\pi$$-base whose elements have an H-closed closure. ACTA MATHEMATICA HUNGARICA, 173(2), 448-460 [10.1007/s10474-024-01450-x].

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

Giacopello, D.
2024-08-22

Abstract

We deal with the class of Hausdorff spaces having a π-base whose elements have an H-closed closure. Carlson proved that |X| ≤ 2 wL(X)ψc(X)t(X) for every quasiregular space X with a π-base whose elements have an H-closed closure. We provide an example of a space X having a π-base whose elements have an H-closed closure which is not quasiregular (neither Urysohn) such that |X| > 2 wL(X)χ(X) (then |X| > 2 wL(X)ψc(X)t(X) ). Always in the class of spaces with a π-base whose elements have an H-closed closure, we establish the bound |X| ≤ 2 wL(X)k(X) for Urysohn spaces and we give an example of an Urysohn space Z such that k(Z) < χ(Z). Lastly, we present some equivalent conditions to the Martin’s Axiom involving spaces with a π-base whose elements have an H-closed closure and, additionally, we prove that if a quasiregular space has a π-base whose elements have an H-closed closure then such a space is Baire.
22-ago-2024
Settore MATH-02/B - Geometria
Giacopello, D. (2024). On spaces with a $$\pi$$-base whose elements have an H-closed closure. ACTA MATHEMATICA HUNGARICA, 173(2), 448-460 [10.1007/s10474-024-01450-x].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10447/666665
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