Том 71
№ 11

All Issues

Balleans and G -spaces

Petrenko O. V., Protasov I. V.

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We show that every ballean (equivalently, coarse structure) on a set $X$ can be determined by some group $G$ of permutations of $X$ and some group ideal $\mathcal{I}$ on $G$. We refine this characterization for some basic classes of balleans: metrizable, cellular, graph, locally finite, and uniformly locally finite. Then we show that a free ultrafilter $\mathcal{U}$ on $\omega$ is a $T$-point with respect to the class of all metrizable locally finite balleans on $\omega$ if and only if $\mathcal{U}$ is a $Q$-point. The paper is concluded with а list of open questions.

English version (Springer): Ukrainian Mathematical Journal 64 (2012), no. 3, pp 387-393.

Citation Example: Petrenko O. V., Protasov I. V. Balleans and G -spaces // Ukr. Mat. Zh. - 2012. - 64, № 3. - pp. 344-350.

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