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More than a 0-point. (English) Zbl 1150.54025
Summary: We construct in ZFC an ultrafilter $$\mathcal U \in \mathbb N^{\ast }$$ such that for every one-to-one function $$f\: \mathbb N\rightarrow \mathbb N$$ there exists $$U\in \mathcal U$$ with $$f[U]$$ in the summable ideal, i.e. the sum of reciprocals of its elements converges. This strengthens Gryzlov’s result concerning the existence of $$0$$-points.

##### MSC:
 54D40 Remainders in general topology 54G99 Peculiar topological spaces
##### Keywords:
ultrafilter; $$0$$-point; summable ideal; linked family
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