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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 unitary Cauchy filters on topological monoids

Boris G. Averbukh (2013)

Topological Algebra and its Applications

For Hausdorff topological monoids, the concept of a unitary Cauchy net is a generalization of the concept of a fundamental sequence of reals. We consider properties and applications of such nets and of corresponding filters and prove, in particular, that the underlying set of a given monoid, endowed with the family of such filters, forms a Cauchy space whose convergence structure defines a uniform topology. A commutative monoid endowed with the corresponding uniformity is uniform. A distant purpose...

On unitary extensions and unitary completions of topological monoids

Boris G. Averbukh (2016)

Topological Algebra and its Applications

The concept of a unitary Cauchy net in an arbitrary Hausdorff topological monoid generalizes the concept of a fundamental sequence of reals. We construct extensions of this monoid where all its unitary Cauchy nets converge.

Openly factorizable spaces and compact extensions of topological semigroups

Taras O. Banakh, Svetlana Dimitrova (2010)

Commentationes Mathematicae Universitatis Carolinae

We prove that the semigroup operation of a topological semigroup S extends to a continuous semigroup operation on its Stone-Čech compactification β S provided S is a pseudocompact openly factorizable space, which means that each map f : S Y to a second countable space Y can be written as the composition f = g p of an open map p : X Z onto a second countable space Z and a map g : Z Y . We present a spectral characterization of openly factorizable spaces and establish some properties of such spaces.

Ordered Cauchy spaces.

Kent, Darrell C., Vainio, R. (1985)

International Journal of Mathematics and Mathematical Sciences

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