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In this article we analyze the notions of amenability and paradoxical decomposition from an algebraic perspective. We consider this dichotomy for locally finite extended metric spaces and for general algebras over commutative fields. In the…

Rings and Algebras · Mathematics 2018-08-08 Pere Ara , Kang Li , Fernando Lledó , Jianchao Wu

In this paper we characterize the sectional category of subgroup inclusions and the $r^{th}$-sequential topological complexity of aspherical spaces of a group G in terms of the A-genus in the sense of Clapp-Puppe and Bartsch for a suitable…

Algebraic Topology · Mathematics 2025-02-18 Arturo Espinosa Baro

The aim of this paper is to study the $(\alpha, \gamma)$-prolongation of central extensions. We obtain the obstruction theory for $(\alpha, \gamma)$-prolongations and classify $(\alpha, \gamma)$-prolongations thanks to low-dimensional…

Group Theory · Mathematics 2013-01-09 Nguyen Tien Quang , Che T. Kim Phung , Pham Thi Cuc

Given an additive equational category with a closed symmetric monoidal structure and a potential dualizing object, we find sufficient conditions that the category of topological objects over that category has a good notion of full…

Category Theory · Mathematics 2016-09-15 Michael Barr

The goal of this article is to study results and examples concerning finitely presented covers of finitely generated amenable groups. We collect examples of groups $G$ with the following properties: (i) $G$ is finitely generated, (ii) $G$…

Group Theory · Mathematics 2013-05-06 Mustafa Gokhan Benli , Rostislav Grigorchuk , Pierre De La Harpe

We give a classification of open equivariant topological conformal field theories in terms of Calabi-Yau $A_\infty$-categories endowed with a group action.

Algebraic Topology · Mathematics 2015-12-14 Ramses Fernandez-Valencia

Automorphisms of structural matrix algebras in block upper triangular form has been studied recently in \cite{Akkurt E-M Barker 2}, and this work is a follow-up paper of that study. The aim of this paper is to explain the topic in a much…

Rings and Algebras · Mathematics 2014-11-05 Emira Akkurt , Mustafa Akkurt

The author determines the structure of automorphism groups of smooth plane curves of degree at least four. Furthermore, he gives some upper bounds for the order of automorphism groups of smooth plane curves and classifies the cases with…

Algebraic Geometry · Mathematics 2014-06-10 Takeshi Harui

In this article, we focus on a new perspective of automorphisms of complex 2-tori, reviewing previous works from a lattice-theoretic point of view. In particular, we give a classification of families of symplectic and non-symplectic…

Algebraic Geometry · Mathematics 2015-06-19 Giovanni Mongardi , Kévin Tari , Malte Wandel

We prove that if a normal subgroup of the extended mapping class group of a closed surface has an element of sufficiently small support then its automorphism group and abstract commensurator group are both isomorphic to the extended mapping…

Geometric Topology · Mathematics 2018-05-10 Tara Brendle , Dan Margalit

We show that elementary amenable groups, which have a bound on the orders of their finite subgroups, admit a finite dimensional model for the classifying space with virtually cyclic isotropy.

Group Theory · Mathematics 2012-01-20 Martin Fluch , Brita E. A. Nucinkis

In this paper, we study the isotropy subgroups of some almost rigid domains and give necessary and sufficient conditions for an automorphism to be in the isotropy subgroup.

Commutative Algebra · Mathematics 2022-02-22 Nikhilesh Dasgupta , Animesh Lahiri

The superextension $\lambda(X)$ of a set $X$ consists of all maximal linked families on $X$. Any associative binary operation $*: X\times X \to X$ can be extended to an associative binary operation $*:…

Group Theory · Mathematics 2020-04-09 Taras Banakh , Volodymyr Gavrylkiv

We consider possibly singular rational projective k*-surfaces and provide an explicit description of the unit component of the automorphism group in terms of isotropy group orders and intersection numbers of suitable invariant curves. As an…

Algebraic Geometry · Mathematics 2020-12-02 Juergen Hausen , Timo Hummel

This article investigates a few questions about orbits of local automorphisms in manifolds endowed with rigid geometric structures. We give sufficient conditions for local homogeneity in a broad class of such structures, namely Cartan…

Differential Geometry · Mathematics 2020-05-20 Vincent Pecastaing

We investigate characterizations of the Galois connection sInv-Aut between sets of finitary relations on a base set A and their automorphisms. In particular, for A=omega_1, we construct a countable set R of relations that is closed under…

Logic · Mathematics 2007-05-23 Ferdinand Börner , Martin Goldstern , Saharon Shelah

We examine the topological dynamics of the automorphism groups of omega-categorical sparse graphs resulting from Hrushovski constructions. Specifically, we consider the fixed points on type spaces property, which a structure M has if, for…

Logic · Mathematics 2024-08-14 Rob Sullivan

We show that the canonical map from the associative operad to the unital associative operad is a homotopy epimorphism for a wide class of symmetric monoidal model categories. As a consequence, the space of unital associative algebra…

Algebraic Topology · Mathematics 2016-01-27 Fernando Muro

We investigate the structure of the monoid of endomorphisms of the ordered set $(\mathbb{Q},{\leq})$ of rational numbers. We show that for any countable linearly ordered set $\Omega$, there are uncountably many maximal subgroups of…

Group Theory · Mathematics 2018-07-04 Jillian D. McPhee , James D. Mitchell , Martyn Quick

Let $G$ be a finite group acting on a connected compact surface $\Sigma$, and $M$ be an integer homology 3-sphere. We show that if each element of $G$ is extendable over $M$ with respect to a fixed embedding $\Sigma\rightarrow M$, then $G$…

Geometric Topology · Mathematics 2020-03-27 Yi Ni , Chao Wang , Shicheng Wang