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Rare α -continuity.

Jafari, Saeid (2005)

Bulletin of the Malaysian Mathematical Sciences Society. Second Series

Rectangular covers of products missing diagonals

Yukinobu Yajima (1994)

Commentationes Mathematicae Universitatis Carolinae

We give a characterization of a paracompact Σ -space to have a G δ -diagonal in terms of three rectangular covers of X 2 Δ . Moreover, we show that a local property and a global property of a space X are given by the orthocompactness of ( X × β X ) Δ .

Relations approximated by continuous functions in the Vietoris topology

L'. Holá, R. A. McCoy (2007)

Fundamenta Mathematicae

Let X be a Tikhonov space, C(X) be the space of all continuous real-valued functions defined on X, and CL(X×ℝ) be the hyperspace of all nonempty closed subsets of X×ℝ. We prove the following result: Let X be a locally connected locally compact paracompact space, and let F ∈ CL(X×ℝ). Then F is in the closure of C(X) in CL(X×ℝ) with the Vietoris topology if and only if: (1) for every x ∈ X, F(x) is nonempty; (2) for every x ∈ X, F(x) is connected; (3) for every isolated x ∈ X, F(x) is a singleton...

Relative Compactness for Hyperspaces

Sianesi, Francesca (1999)

Serdica Mathematical Journal

The present paper contains results characterizing relatively compact subsets of the space of the closed subsets of a metrizable space, equipped with various hypertopologies. We investigate the hyperspace topologies that admit a representation as weak topologies generated by families of gap functionals defined on closed sets, as well as hit-and-miss topologies and proximal-hit and-miss topologies.

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