On Szymański theorem on hereditary normality of \beta\omega

[摘要] We discuss the following result of A. Szymański in ``Retracts and non-normality points" (2012), Corollary 3.5.: If F is a closed subspace of \omega ^{*} and the \pi-weight of F is countable, then every nonisolated point of F is a non-normality point of \omega ^{*}. We obtain stronger results for all types of points, excluding the limits of countable discrete sets considered in ``Some non-normal subspaces of the Čech-Stone compactification of a discrete space" (1980) by A. Błaszczyk and A. Szymański. Perhaps our proofs look ``more natural in this area".

[学科分类] 物理化学和理论化学

[关键词] Čech-Stone compactification;non-normality point;butterfly-point;countable \pi-weight