On small profinite groups

2015/11/27 by Patrick Helbig, Helbig, Patrick
Mathematics · #FOS: Mathematics #Group Theory (math.GR) #Logic (math.LO) #math.GR #math.LO

paper · pdf · doi:10.48550/arxiv.1511.08760

Previously titled "Small profinite groups and their elementary theory"; extended Question 3.15

arxiv created 2015/12/28 · arxiv updated 2015/12/29

Abstract

A profinite group is called small if it has only finitely many open subgroups of index n for each positive integer n. We show that every Frattini cover of a small profinite group is small. A profinite group is called strongly complete if every subgroup of finite index is open. We show that two profinite groups that are elementarily equivalent, in the first-order language of groups, are isomorphic if one of them is strongly complete, extending a result of Moshe Jarden and Alexander Lubotzky which treats the case of finitely generated profinite groups.

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