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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
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