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Extraresolvability and cardinal arithmetic

Ofelia Teresa Alas, Salvador García-Ferreira, Artur Hideyuki Tomita (1999)

Commentationes Mathematicae Universitatis Carolinae

Following Malykhin, we say that a space X is extraresolvable if X contains a family 𝒟 of dense subsets such that | 𝒟 | > Δ ( X ) and the intersection of every two elements of 𝒟 is nowhere dense, where Δ ( X ) = min { | U | : U is a nonempty open subset of X } is the dispersion character of X . We show that, for every cardinal κ , there is a compact extraresolvable space of size and dispersion character 2 κ . In connection with some cardinal inequalities, we prove the equivalence of the following statements: 1) 2 κ < 2 κ + , 2) ( κ + ) κ is extraresolvable and...

Extraresolvability of balleans

Igor V. Protasov (2007)

Commentationes Mathematicae Universitatis Carolinae

A ballean is a set endowed with some family of balls in such a way that a ballean can be considered as an asymptotic counterpart of a uniform topological space. We introduce and study a new cardinal invariant of a ballean, the extraresolvability, which is an asymptotic reflection of the corresponding invariant of a topological space.

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