A semifilter approach to selection principles II: $\tau ^\ast $-covers

Lubomyr Zdomsky

Displaying similar documents to “A semifilter approach to selection principles II: $τ^{*}$ -covers”

On meager function spaces, network character and meager convergence in topological spaces

Taras O. Banakh, Volodymyr Mykhaylyuk, Lubomyr Zdomsky (2011)

Commentationes Mathematicae Universitatis Carolinae

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For a non-isolated point $x$ of a topological space $X$ let ${nw}_{χ} (x)$ be the smallest cardinality of a family $𝒩$ of infinite subsets of $X$ such that each neighborhood $O (x) \subset X$ of $x$ contains a set $N \in 𝒩$ . We prove that (a) each infinite compact Hausdorff space $X$ contains a non-isolated point $x$ with ${nw}_{χ} (x) = ℵ_{0}$ ; (b) for each point $x \in X$ with ${nw}_{χ} (x) = ℵ_{0}$ there is an injective sequence ${(x_{n})}_{n \in ω}$ in $X$ that $ℱ$ -converges to $x$ for some meager filter $ℱ$ on $ω$ ; (c) if a functionally Hausdorff space $X$ contains an $ℱ$ -convergent injective sequence for some...

Some observations on filters with properties defined by open covers

Rodrigo Hernández-Gutiérrez, Paul J. Szeptycki (2015)

Commentationes Mathematicae Universitatis Carolinae

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We study the relation between the Hurewicz and Menger properties of filters considered topologically as subspaces of $𝒫 (ω)$ with the Cantor set topology.

The point of continuity property, neighbourhood assignments and filter convergences

Ahmed Bouziad (2012)

Fundamenta Mathematicae

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We show that for some large classes of topological spaces X and any metric space (Z,d), the point of continuity property of any function f: X → (Z,d) is equivalent to the following condition: (*) For every ε > 0, there is a neighbourhood assignment ${(V_{x})}_{x \in X}$ of X such that d(f(x),f(y)) < ε whenever $(x, y) \in V_{y} \times V_{x}$ . We also give various descriptions of the filters ℱ on the integers ℕ for which (*) is satisfied by the ℱ-limit of any sequence of continuous functions from a topological space into a metric...

Guessing clubs in the generalized club filter

Bernhard König, Paul Larson, Yasuo Yoshinobu (2007)

Fundamenta Mathematicae

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We present principles for guessing clubs in the generalized club filter on $_{κ} λ$ . These principles are shown to be weaker than classical diamond principles but often serve as sufficient substitutes. One application is a new construction of a λ⁺-Suslin-tree using assumptions different from previous constructions. The other application partly solves open problems regarding the cofinality of reflection points for stationary subsets of ${[λ]}^{ℵ ₀}$ .

Products of topological spaces and families of filters

Paolo Lipparini (2023)

Commentationes Mathematicae Universitatis Carolinae

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We show that, under suitably general formulations, covering properties, accumulation properties and filter convergence are all equivalent notions. This general correspondence is exemplified in the study of products. We prove that a product is Lindelöf if and only if all subproducts by $\leq ω_{1}$ factors are Lindelöf. Parallel results are obtained for final $ω_{n}$ -compactness, $[λ, μ]$ -compactness, the Menger and the Rothberger properties.

Displaying similar documents to “A semifilter approach to selection principles II: τ * -covers”

On meager function spaces, network character and meager convergence in topological spaces

Some observations on filters with properties defined by open covers

The point of continuity property, neighbourhood assignments and filter convergences

Guessing clubs in the generalized club filter

Products of topological spaces and families of filters

Displaying similar documents to “A semifilter approach to selection principles II: $τ^{*}$ -covers”