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Separating sets by Darboux-like functions

Aleksander Maliszewski (2002)

Fundamenta Mathematicae

We consider the following problem: Characterize the pairs ⟨A,B⟩ of subsets of ℝ which can be separated by a function from a given class, i.e., for which there exists a function f from that class such that f = 0 on A and f = 1 on B (the classical separation property) or f < 0 on A and f > 0 on B (a new separation property).

Sequential completeness of subspaces of products of two cardinals

Roman Frič, Nobuyuki Kemoto (1999)

Czechoslovak Mathematical Journal

Let κ be a cardinal number with the usual order topology. We prove that all subspaces of κ 2 are weakly sequentially complete and, as a corollary, all subspaces of ω 1 2 are sequentially complete. Moreover we show that a subspace of ( ω 1 + 1 ) 2 need not be sequentially complete, but note that X = A × B is sequentially complete whenever A and B are subspaces of κ .

Sequential continuity on dyadic compacta and topological groups

Aleksander V. Arhangel'skii, Winfried Just, Grzegorz Plebanek (1996)

Commentationes Mathematicae Universitatis Carolinae

We study conditions under which sequentially continuous functions on topological spaces and sequentially continuous homomorphisms of topological groups are continuous.

Sums of quasicontinuous functions

Ján Borsík (1993)

Mathematica Bohemica

It is proved that every real cliquish function defined on a separable metrizable space is the sum of three quasicontinuous functions.

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