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Strong remote points

Sergei Logunov — 2002

Commentationes Mathematicae Universitatis Carolinae

Remote points constructed so far are actually strong remote. But we construct remote points of another type.

Non-normality points and nice spaces

Sergei Logunov — 2021

Commentationes Mathematicae Universitatis Carolinae

J. Terasawa in " β X - { p } are non-normal for non-discrete spaces X " (2007) and the author in “On non-normality points and metrizable crowded spaces” (2007), independently showed for any metrizable crowded space X that each point p of its Čech–Stone remainder X * is a non-normality point of β X . We introduce a new class of spaces, named nice spaces, which contains both of Sorgenfrey line and every metrizable crowded space. We obtain the result above for every nice space.

On non-normality points, Tychonoff products and Suslin number

Sergei Logunov — 2022

Commentationes Mathematicae Universitatis Carolinae

Let a space X be Tychonoff product α < τ X α of τ -many Tychonoff nonsingle point spaces X α . Let Suslin number of X be strictly less than the cofinality of τ . Then we show that every point of remainder is a non-normality point of its Čech–Stone compactification β X . In particular, this is true if X is either R τ or ω τ and a cardinal τ is infinite and not countably cofinal.

On Szymański theorem on hereditary normality of β ω

Sergei Logunov — 2022

Commentationes Mathematicae Universitatis Carolinae

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 ω * and the π -weight of F is countable, then every nonisolated point of F is a non-normality point of ω * . 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...

On butterfly-points in β X , Tychonoff products and weak Lindelöf numbers

Sergei Logunov — 2022

Commentationes Mathematicae Universitatis Carolinae

Let X be the Tychonoff product α < τ X α of τ -many Tychonoff non-single point spaces X α . Let p X * be a point in the closure of some G X whose weak Lindelöf number is strictly less than the cofinality of τ . Then we show that β X { p } is not normal. Under some additional assumptions, p is a butterfly-point in β X . In particular, this is true if either X = ω τ or X = R τ and τ is infinite and not countably cofinal.

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