English

Topologically independent sets in precompact groups

General Topology 2017-12-08 v2

Abstract

It is a simple fact that a subgroup generated by a subset AA of an abelian group is the direct sum of the cyclic groups a\langle a\rangle, aAa\in A if and only if the set AA is independent. In [5] the concept of an independentindependent set in an abelian group was generalized to a topologicallytopologically independentindependent setset in a topological abelian group (these two notions coincide in discrete abelian groups). It was proved that a topological subgroup generated by a subset AA of an abelian topological group is the Tychonoff direct sum of the cyclic topological groups a\langle a\rangle, aAa\in A if and only if the set AA is topologically independent and absolutely Cauchy summable. Further, it was shown, that the assumption of absolute Cauchy summability of AA can not be removed in general in this result. In our paper we show that it can be removed in precompact groups. In other words, we prove that if AA is a subset of a {\em precompact} abelian group, then the topological subgroup generated by AA is the Tychonoff direct sum of the topological cyclic subgroups a\langle a\rangle, aAa\in A if and only if AA is topologically independent. We show that precompactness can not be replaced by local compactness in this result.

Keywords

Cite

@article{arxiv.1703.04102,
  title  = {Topologically independent sets in precompact groups},
  author = {Jan Spevak},
  journal= {arXiv preprint arXiv:1703.04102},
  year   = {2017}
}
R2 v1 2026-06-22T18:43:25.892Z