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It is proved that every finitely generated profinite group with fewer than $2^{\aleph_0}$ conjugacy classes of elements of infinite order is finite

Group Theory · Mathematics 2022-09-30 John S. Wilson

We determine the structure of the finite groups with the property that every cyclic subgroup is the intersection of maximal subgroups, comparing this property with the one where all proper subgroups are intersections of maximal subgroups.

Group Theory · Mathematics 2025-08-07 Andrea Lucchini

A subgroup $\Delta\leq \Gamma$ is commensurated if $|\Delta:\Delta\cap \gamma\Delta\gamma^{-1}|<\infty$ for all $\gamma\in \Gamma$. We show a finitely generated branch group is just infinite if and only if every commensurated subgroup is…

Group Theory · Mathematics 2016-07-27 Phillip Wesolek

In response to a question raised by Belolipetsky and the first author, we prove that for every finite group $G$ there are infinitely many isomorphism classes of compact complex hyperbolic $2$-manifolds with automorphism group isomorphic to…

Geometric Topology · Mathematics 2025-12-23 Alexander Lubotzky , Matthew Stover

A subset S of a group G invariably generates G if G = <s^(g(s)) | s in S> for each choice of g(s) in G, s in S. In this paper we study invariable generation of infinite groups, with emphasis on linear groups. Our main result shows that a…

Group Theory · Mathematics 2014-07-18 William M. Kantor , Alexander Lubotzky , Aner Shalev

If a finite group G has a presentation with d generators and r relations, it is well-known that r - d is at least the rank of the Schur multiplier of G; a presentation is called efficient if equality holds. There is an analogous definition…

Group Theory · Mathematics 2009-05-05 R. M. Guralnick , W. M. Kantor , M. Kassabov , A. Lubotzky

We introduce and study the concept of cyclicity degree of a finite group $G$. This quantity measures the probability of a random subgroup of $G$ to be cyclic. Explicit formulas are obtained for some particular classes of finite groups. An…

Group Theory · Mathematics 2015-04-08 Marius Tărnăuceanu , László Tóth

We introduce and investigate a class of profinite groups defined via extensions of centralizers analogous to the extensively studied class of finitely generated fully residually free groups, that is, limit groups (in the sense of Z. Sela).…

Group Theory · Mathematics 2017-11-07 Pavel Zalesskii , Theo Zapata

We introduce a class $\A$ of finitely generated residually finite accessible groups with some natural restriction on one-ended vertex groups in their JSJ-decompositions. We prove that the profinite completion of groups in $\A$ almost…

Group Theory · Mathematics 2022-08-30 Vagner R. de Bessa , Anderson L. P. Porto , Pavel A. Zalesskii

We show that the class of profinite duality groups is closed under group extensions provided that the kernel satisfies some finiteness condition. This extends earlier results of Pletch and of Wingberg.

Group Theory · Mathematics 2008-09-26 Alexander Schmidt , Kay Wingberg

We give a characterization of toral relatively hyperbolic virtually special groups in terms of the profinite completion. We also prove a Tits alternative for subgroups of the profinite completion $\hat G$ of a relatively hyperbolic…

Group Theory · Mathematics 2025-03-18 Pavel Zalesskii

There has been much recent interest into those properties of a 3-manifold determined by the profinite completion of its fundamental group. In this paper we give readily computable criteria specifying precisely when two orientable graph…

Geometric Topology · Mathematics 2017-03-16 Gareth Wilkes

We identify the simple algebraic groups over number fields that are, in a suitable sense, determined by their finite adele points. Assuming CSP and Grothendieck rigidity, our results essentially characterize higher rank arithmetic groups…

Group Theory · Mathematics 2026-05-06 Adrian Baumann , Holger Kammeyer

We investigate when the clone of congruence preserving functions is finitely generated. We obtain a full description for all finite $p$-groups, and for all finite algebras with Mal'cev term and simple congruence lattice. The…

Rings and Algebras · Mathematics 2019-09-04 Erhard Aichinger , Marijana Lazić , Nebojša Mudrinski

We investigate the ability of a free pro-$\CC$ group of infinite rank to abstractly solve abstract embedding problems, and conclude that for some varieties $\CC$, the profinite completion of any order, of a free pro-$\CC$ group of infinite…

Group Theory · Mathematics 2023-01-31 Tamar Bar-On

Surface groups are determined among limit groups by their profinite completions. As a corollary, the set of surface words in a free group is closed in the profinite topology.

Group Theory · Mathematics 2020-10-16 Henry Wilton

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…

Group Theory · Mathematics 2015-12-29 Patrick Helbig

Let $(\mathcal{G},\Gamma)$ be an abstract graph of finite groups. If $\Gamma$ is finite, we can construct a profinite graph of groups in a natural way $(\hat{\mathcal{G}},\Gamma)$, where $\hat{\mathcal{G}}(m)$ is the profinite completion of…

Group Theory · Mathematics 2021-05-07 Mattheus Aguiar , Pavel Zalesski

Let $S$ be a finitely generated pro-$p$ group. Let $\Emb(S)$ be the class of profinite groups $G$ that have $S$ as a Sylow subgroup, and such that $S$ intersects non-trivially with every non-trivial normal subgroup of $G$. In this paper, we…

Group Theory · Mathematics 2013-01-11 Colin D. Reid

In this note we show that various (geometric/homological) finiteness properties are not profinite properties. For example for every $1 \le k, \ell \le \bbn$, there exist two finitely generated residually finite groups $\Ga_1$ and $\Ga_2$…

Group Theory · Mathematics 2012-11-29 Alexander Lubotzky