错误:搜索内容不能为空,请输入英文关键词
错误:关键词超出字数限制,请精简
高级检索

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

  • D. Giacopello

摘要

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