Abstract
Given a topological group G that can be embedded as a topological subgroup into some topological vector space (over the field of reals) we say that G has invariant linear span if all linear spans of G under arbitrary embeddings into topological vector spaces are isomorphic as topological vector spaces. For an arbitrary set A let \({{\mathbb {Z}}}^{(A)}\) be the direct sum of |A|-many copies of the discrete group of integers endowed with the Tychonoff product topology. We show that the topological group \({{\mathbb {Z}}}^{(A)}\) has invariant linear span. This answers a question from a paper of Dikranjan et al. (J Math Anal Appl 437:1257–1282, 2016) in positive. We prove that given a non-discrete sequential space X, the free abelian topological group A(X) over X is an example of a topological group that embeds into a topological vector space but does not have invariant linear span.
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Acknowledgements
The authors would like to thank the anonymous reviewers for careful reading of the paper and for correcting some of the references.
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Eva Pernecká was supported by the Grant GAČR 18-00960Y of the Czech Science Foundation.
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Pernecká, E., Spěvák, J. Topological groups with invariant linear spans. Rev Mat Complut 35, 219–226 (2022). https://doi.org/10.1007/s13163-020-00383-7
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DOI: https://doi.org/10.1007/s13163-020-00383-7
Keywords
- Topological group
- Topological vector space
- Embedding
- Absolutely Cauchy summable
- Topologically independent
- Diophantine approximation