A construction of a Fréchet-Urysohn space, and some convergence concepts

Aleksander V. Arhangel'skii

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Countable fan-tightness versus countable tightness

Aleksander V. Arhangel&#039;skii, Angelo Bella (1996)

Commentationes Mathematicae Universitatis Carolinae

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Countable tightness is compared to the stronger notion of countable fan-tightness. In particular, we prove that countable tightness is equivalent to countable fan-tightness in countably compact regular spaces, and that countable fan-tightness is preserved by pseudo-open compact mappings. We also discuss the behaviour of countable tightness and of countable fan-tightness under the product operation.

Point countable open coverings in countably compact spaces

Aquaro, G.

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A new way to find compact zero-dimensional first countable preimages of first countable compact spaces

Vladimir Vladimirovich Tkachuk (1988)

Commentationes Mathematicae Universitatis Carolinae

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First countable and countable spaces all compactifications of which contain βN

Eric van Douwen, Teodor Przymusiński (1979)

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First countable spaces without point-countable π-bases

István Juhász, Lajos Soukup, Zoltán Szentmiklóssy (2007)

Fundamenta Mathematicae

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We answer several questions of V. Tkachuk [Fund. Math. 186 (2005)] by showing that ∙ there is a ZFC example of a first countable, 0-dimensional Hausdorff space with no point-countable π-base (in fact, the minimum order of a π-base of the space can be made arbitrarily large); ∙ if there is a κ-Suslin line then there is a first countable GO-space of cardinality κ⁺ in which the order of any π-base is at least κ; ∙ it is consistent to have a...