Countable tightness is not discretely reflexive in $$\sigma$$-compact spaces

Abstract Answering a question raised by V.V. Tkachuk in [10], we present several examples of $$\sigma$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>σ</mml:mi> </mml:math> -compact spaces, some only consistent and some in ZFC, that are not countably tight but in which the closure of any discrete subset is countably tight. In fact, in some of our examples the closures of all discrete subsets are even first countable.

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Publication Details

Journal
Acta Mathematica Academiae Scientiarum Hungaricae
Published
2025-03-28
DOI
https://doi.org/10.1007/s10474-025-01521-7
Primary Topic
Advanced Topology and Set Theory
Type
article
Field-Weighted Citation Impact
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article

Countable tightness is not discretely reflexive in $$\sigma$$-compact spaces

J. van Mill, István Juhász
1 links
Acta Mathematica Academiae Scientiarum Hungaricae
Advanced Topology and Set Theory
article

Countable tightness is not discretely reflexive in $$\sigma$$-compact spaces

J. van Mill, István Juhász
article en

Abstract

Abstract Answering a question raised by V.V. Tkachuk in [10], we present several examples of $$\sigma$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>σ</mml:mi> </mml:math> -compact spaces, some only consistent and some in ZFC, that are not countably tight but in which the closure of any discrete subset is countably tight. In fact, in some of our examples the closures of all discrete subsets are even first countable.

Acta Mathematica Academiae Scientiarum HungaricaeVol. 175(2)
HUN-REN Alfréd Rényi Institute of Mathematics (HU), University of Amsterdam (NL)
Openalex Percentile: Top 89%
Advanced Topology and Set Theory
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