Displaying similar documents to “Extension of multisequences and countably uniradial classes of topologies”

Ordinal ultrafilters versus P-hierarchy

Andrzej Starosolski (2014)

Open Mathematics

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An earlier paper [Starosolski A., P-hierarchy on βω, J. Symbolic Logic, 2008, 73(4), 1202–1214] investigated the relations between ordinal ultrafilters and the so-called P-hierarchy. The present paper focuses on the aspects of characterization of classes of ultrafilters of finite index, existence, generic existence and the Rudin-Keisler-order.

Strongly sequential spaces

Frédéric Mynard (2000)

Commentationes Mathematicae Universitatis Carolinae

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The problem of Y. Tanaka [10] of characterizing the topologies whose products with each first-countable space are sequential, is solved. The spaces that answer the problem are called strongly sequential spaces in analogy to strongly Fréchet spaces.