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On finite powers of countably compact groups

Artur Hideyuki Tomita (1996)

Commentationes Mathematicae Universitatis Carolinae

We will show that under M A c o u n t a b l e for each k there exists a group whose k -th power is countably compact but whose 2 k -th power is not countably compact. In particular, for each k there exists l [ k , 2 k ) and a group whose l -th power is countably compact but the l + 1 -st power is not countably compact.

On locales whose countably compact sublocales have compact closure

Themba Dube (2023)

Mathematica Bohemica

Among completely regular locales, we characterize those that have the feature described in the title. They are, of course, localic analogues of what are called cl -isocompact spaces. They have been considered in T. Dube, I. Naidoo, C. N. Ncube (2014), so here we give new characterizations that do not appear in this reference.

On maps preserving connectedness and/or compactness

István Juhász, Jan van Mill (2018)

Commentationes Mathematicae Universitatis Carolinae

We call a function f : X Y P-preserving if, for every subspace A X with property P, its image f ( A ) also has property P. Of course, all continuous maps are both compactness- and connectedness-preserving and the natural question about when the converse of this holds, i.e. under what conditions such a map is continuous, has a long history. Our main result is that any nontrivial product function, i.e. one having at least two nonconstant factors, that has connected domain, T 1 range, and is connectedness-preserving...

On n -thin dense sets in powers of topological spaces

Adam Bartoš (2016)

Commentationes Mathematicae Universitatis Carolinae

A subset of a product of topological spaces is called n -thin if every its two distinct points differ in at least n coordinates. We generalize a construction of Gruenhage, Natkaniec, and Piotrowski, and obtain, under CH, a countable T 3 space X without isolated points such that X n contains an n -thin dense subset, but X n + 1 does not contain any n -thin dense subset. We also observe that part of the construction can be carried out under MA.

On powers of Lindelöf spaces

Isaac Gorelic (1994)

Commentationes Mathematicae Universitatis Carolinae

We present a forcing construction of a Hausdorff zero-dimensional Lindelöf space X whose square X 2 is again Lindelöf but its cube X 3 has a closed discrete subspace of size 𝔠 + , hence the Lindelöf degree L ( X 3 ) = 𝔠 + . In our model the Continuum Hypothesis holds true. After that we give a description of a forcing notion to get a space X such that L ( X n ) = 0 for all positive integers n , but L ( X 0 ) = 𝔠 + = 2 .

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