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In 'The essentially chief series of a compactly generated locally compact group', an analogue of chief series for finite groups is discovered for compactly generated locally compact groups. In the present article, we show that chief factors…

Group Theory · Mathematics 2017-12-06 Colin D. Reid , Phillip R. Wesolek

In this note we present that the patch counting entropy can be obtained as a limit and investigate which sequences of compact sets are suitable to define this quantity. We furthermore present a geometric definition of patch counting entropy…

Dynamical Systems · Mathematics 2020-11-26 Till Hauser

We obtain many results and solve some problems about feebly compact paratopological groups. We obtain necessary and sufficient conditions for such a group to be topological. One of them is the quasiregularity. We prove that each…

Group Theory · Mathematics 2020-08-05 Taras Banakh , Alex Ravsky

A Hausdorff topological group is called minimal if it does not admit a strictly coarser Hausdorff group topology. This paper mostly deals with the topological group $H_+(X)$ of order-preserving homeomorphisms of a compact linearly ordered…

General Topology · Mathematics 2015-06-19 Michael Megrelishvili , Luie Polev

We give a topological framework for the study of Sela's limit groups: limit groups are limits of free groups in a compact space of marked groups. Many results get a natural interpretation in this setting. The class of limit groups is known…

Group Theory · Mathematics 2007-05-23 Christophe Champetier , Vincent Guirardel

We first give simplified and corrected accounts of some results in \cite{PiRCP} on compactifications of pseudofinite groups. For instance, we use a classical theorem of Turing \cite{Turing} to give a simplified proof that any definable…

Logic · Mathematics 2025-06-18 Gabriel Conant , Ehud Hrushovski , Anand Pillay

Following Isaacs (see [Isa08, p. 94]), we call a normal subgroup N of a finite group G large, if $C_G(N) \leq N$, so that N has bounded index in G. Our principal aim here is to establish some general results for systematically producing…

Group Theory · Mathematics 2019-06-18 Stefanos Aivazidis , Thomas W. Müller

It is a simple fact that a subgroup generated by a subset $A$ of an abelian group is the direct sum of the cyclic groups $\langle a\rangle$, $a\in A$ if and only if the set $A$ is independent. In [5] the concept of an $independent$ set in…

General Topology · Mathematics 2017-12-08 Jan Spevak

A pointwise-elliptic subset of a topological group is one whose elements all generate relatively-compact subgroups. A connected locally compact group has a dense pointwise-elliptic subgroup if and only if it is an extension by a compact…

Group Theory · Mathematics 2025-06-27 Alexandru Chirvasitu

We provide a mathematically rigorous definition of local approximation and demonstrate its applicability to some interesting classes of structures. In particular, we prove that any compact simple Lie group is locally approximated by finite…

Logic · Mathematics 2026-04-02 Boris Zilber

It is well known that every locally compact abelian group L can be decomposed as L_1 \oplus R^n, where L_1 contains a compact-open subgroup. In this paper, we use this decomposition to study the topological group Aut(L) of automorphisms of…

General Topology · Mathematics 2011-10-11 Iian B. Smythe

This work is motivated by the problem of finding locally compact group topologies for piecewise full groups (a.k.a.~ topological full groups). We determine that any piecewise full group that is locally compact in the compact-open topology…

Group Theory · Mathematics 2024-08-27 Alejandra Garrido , Colin D. Reid

A topological space $X$ is defined to have a neighborhood $P$-base at any $x\in X$ from some poset $P$ if there exists a neighborhood base $(U_p[x])_{p\in P}$ at $x$ such that $U_p[x]\subseteq U_{p'}[x]$ for all $p\geq p'$ in $P$. We prove…

General Topology · Mathematics 2021-05-21 Ziqn Feng

We study definably compact definably connected groups definable in a sufficiently saturated real closed field $R$. We introduce the notion of group-generic point for $\bigvee$-definable groups and show the existence of group-generic points…

Logic · Mathematics 2017-05-19 Eliana Barriga

(1) Every infinite, Abelian compact (Hausdorff) group K admits 2^|K|-many dense, non-Haar-measurable subgroups of cardinality |K|. When K is nonmetrizable, these may be chosen to be pseudocompact. (2) Every infinite Abelian group G admits a…

General Topology · Mathematics 2013-10-09 W. W. Comfort , S. U. Raczkowski , F. J. Trigos-Arrieta

A locally normal subgroup in a topological group is a subgroup whose normaliser is open. In this paper, we provide a detailed description of the large-scale structure of closed locally normal subgroups of complete Kac-Moody groups over…

Group Theory · Mathematics 2023-02-16 Pierre-Emmanuel Caprace , Timothée Marquis , Colin D. Reid

A Polish group is said to be locally Roelcke precompact if there is a neighborhood of the identity element that is totally bounded in the Roelcke (or lower) group uniformity. These form a subclass of the locally bounded groups, while…

Group Theory · Mathematics 2018-06-12 Joseph Zielinski

We observe a correspondence between collections of closed subgroups and normal subgroups in totally disconnected locally compact groups. This correspondence is applied to prove structure theorems for two classes of totally disconnected…

Group Theory · Mathematics 2014-05-20 Phillip Wesolek

We give a proof of the existence of generalized definable locally compact models for arbitrary approximate subgroups via an application of topological dynamics in model theory. Our construction is simpler and shorter than the original one…

Logic · Mathematics 2023-11-01 Krzysztof Krupiński , Anand Pillay

The paper is concerned with maximal subgroups of the ample (better known as topological full) groups of homeomorphisms of totally disconnected compact metrizable topological spaces. We describe all maximal subgroups that are stabilizers of…

Group Theory · Mathematics 2024-03-26 Rostislav Grigorchuk , Yaroslav Vorobets