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A Polish group containing a Haar null $F_\sigma$-subgroup that cannot be enlarged to a Haar null $G_\delta$-set

General Topology 2021-11-01 v1 Group Theory

Abstract

Answering a question of Elekes and Vidny\'anszky, we construct a Polish meta-abelian group HH and a subgroup FHF\subset H, which is a Haar null FσF_\sigma-set in HH that cannot be enlarged to a Haar null GδG_\delta-set.

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Cite

@article{arxiv.1604.00150,
  title  = {A Polish group containing a Haar null $F_\sigma$-subgroup that cannot be enlarged to a Haar null $G_\delta$-set},
  author = {Taras Banakh},
  journal= {arXiv preprint arXiv:1604.00150},
  year   = {2021}
}

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2 pages