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The Higman--Thompson groups $V_{n,r}$ consist of piecewise linear automorphisms of $r$ intervals where cut points and slopes are $n$-adic. Szymik and Wahl prove homological stability for this family of groups as $r$ increases, and compute…

Algebraic Topology · Mathematics 2026-01-29 Marie-Camille Delarue

We study homogeneous metric spaces, by which we mean connected, locally compact metric spaces whose isometry group acts transitively. After a review of some classical results, we use the Gleason-Iwasawa-Montgomery-Yamabe-Zippin structure…

Given a 2-manifold, a fundamental question to ask is which groups can be realized as the isometry group of a Riemannan metric of constant curvature on the manifold. In this paper, we give a nearly complete classification of such groups for…

Geometric Topology · Mathematics 2024-03-11 Tarik Aougab , Priyam Patel , Nicholas G. Vlamis

We show that every non-precompact topological group admits a fixed point-free continuous action by affine isometries on a suitable Banach space. Thus, precompact groups are defined by the fixed point property for affine isometric actions on…

Group Theory · Mathematics 2008-11-06 Lionel Nguyen Van Thé , Vladimir G. Pestov

In this paper we consider nonnegatively curved finite dimensional Alexandrov spaces with a non-collapsing condition, i.e., such that unit balls have volumes uniformly bounded from below away from zero. We study the relation between the…

Differential Geometry · Mathematics 2025-04-01 Gioacchino Antonelli , Marco Pozzetta

We describe the development of the theory of automatic groups. We begin with a historical introduction, define the concepts of automatic, biautomatic and combable groups, derive basic properties, then explain how hyperbolic groups and the…

Group Theory · Mathematics 2022-05-31 Sarah Rees

We give a construction of the Gurarij space, analogous to Katetov's construction of the Urysohn space. The adaptation of Katetov's technique uses a generalisation of the Arens-Eells enveloping space to metric space with a distinguished…

Logic · Mathematics 2012-08-14 Itaï Ben Yaacov

A homomorphism from a completely metrizable topological group into a free product of groups whose image is not contained in a factor of the free product is shown to be continuous with respect to the discrete topology on the range. In…

Group Theory · Mathematics 2013-06-12 Konstantin Slutsky

We are considering typed hierarchies of total, continuous functionals using complete, separable metric spaces at the base types. We pay special attention to the so called Urysohn space constructed by P. Urysohn. One of the properties of the…

Logic in Computer Science · Computer Science 2015-07-01 Dag Normann

We study the properly discontinuous and isometric actions on the unit sphere of infinite dimensional Hilbert spaces and we get some new examples of Hilbert manifold with costant positive sectional curvature. We prove some necessary…

Differential Geometry · Mathematics 2007-05-23 Leonardo Biliotti

In this article we prove that the set of torsion-free groups acting by isometries on a hyperbolic metric space whose entropy is bounded above and with a compact quotient is finite. The number of such groups can be estimated in terms of the…

Group Theory · Mathematics 2021-11-09 Gérard Besson , Gilles Courtois , Sylvestre Gallot , Andrea Sambusetti

In this article, we show that the stabilized automorphism group of free exact odometers arising from actions of finitely generated residually finite groups coincides with the topological full group of the odometer acting on itself by right…

Group Theory · Mathematics 2026-01-13 María Isabel Cortez , Vicente Urria

We investigate the local structure of the space $\mathcal{M}$ consisting of isometry classes of compact metric spaces, endowed with the Gromov-Hausdorff metric. We consider finite metric spaces of the same cardinality and suppose that these…

Metric Geometry · Mathematics 2016-11-15 Alexander O. Ivanov , Alexey A. Tuzhilin

The Urysohn space is the unique separable metric space that is universal and homogeneous for finite metric spaces, i.e., it embeds any finite metric space any isometry between finite subspaces extends to an isometry of the whole space. We…

Metric Geometry · Mathematics 2026-01-19 Katrin Tent

We consider an Orlicz space based cohomology for metric (measured) spaces with bounded geometry. We prove the quasi-isometry invariance for a general Young function. In the hyperbolic case, we prove that the degree one cohomology can be…

Metric Geometry · Mathematics 2014-11-25 Matias Carrasco Piaggio

We study several distinguished function algebras on a Polish group $G$, under the assumption that $G$ is Roelcke precompact. We do this by means of the model-theoretic translation initiated by Ben Yaacov and Tsankov: we investigate the…

Logic · Mathematics 2016-02-22 Tomás Ibarlucía

Recall that the Rado graph is the unique countable graph that realizes all one-point extensions of its finite subgraphs. The Rado graph is well-known to be universal and homogeneous in the sense that every isomorphism between finite…

Logic · Mathematics 2018-07-17 Jan Grebík

We are concerned with questions of the following type. Suppose that $G$ and $K$ are topological groups belonging to a certain class $\cal K$ of spaces, and suppose that $\phi:K \to G$ is an abstract (i.e. not necessarily continuous)…

Group Theory · Mathematics 2018-12-06 Oskar Braun , Karl Heinrich Hofmann , Linus Kramer

Persistent homology is a popular and useful tool for analysing finite metric spaces, revealing features that can be used to distinguish sets of unlabeled points and as input into machine learning pipelines. The famous stability theorem of…

Computational Geometry · Computer Science 2024-05-10 Philip Smith , Vitaliy Kurlin

We provide an analysis of the dynamics of isometries and semicontractions of metric spaces. Certain subsets of the boundary at infinity play a fundamental role and are identified completely for the standard boundaries of CAT(0)-spaces,…

Metric Geometry · Mathematics 2014-11-11 Anders Karlsson