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While intersections of convex sets are convex, their unions have rather complicated behavior. Some natural contexts where they appear include duality arguments involving boundaries of convex sets and valuations, which have an Euler…

Combinatorics · Mathematics 2026-02-06 Soohyun Park

Geometrization theorem, fibered case: Every three-manifold that fibers over the circle admits a geometric decomposition. Double limit theorem: for any sequence of quasi-Fuchsian groups whose controlling pair of conformal structures tends…

Geometric Topology · Mathematics 2007-05-23 William P. Thurston

Let G be any finitely generated infinite group. Denote by K(G) the FC-centre of G, i.e., the subgroup of all elements of G whose centralizers are of finite index in G. Let QI(G) denote the group of quasi-isometries of G with respect to word…

Group Theory · Mathematics 2007-05-23 Aniruddha C. Naolekar , Parameswaran Sankaran

In this paper, we state two combination theorems for relatively quasiconvex subgroups in a relatively hyperbolic group. Applications are given to the separability of double cosets of certain relatively quasiconvex subgroups and the…

Group Theory · Mathematics 2013-01-01 Wenyuan Yang

We describe structure of quasihomomorphisms from arbitrary groups to discrete groups. We show that all quasihomomorphisms are 'constructible', i.e., are obtained via certain natural operations from homomorphisms to some groups and…

Group Theory · Mathematics 2015-07-09 Koji Fujiwara , Michael Kapovich

We work in a first-order setting where structures are spread out over a metric space, with quantification allowed only over bounded subsets. Assuming a doubling property for the metric space, we define a canonical {\em core} $\mathcal{J}$…

Logic · Mathematics 2022-02-23 Ehud Hrushovski

We show the equivalence of several characterizations of relative hyperbolicity for metric spaces, and obtain extra information about geodesics in a relatively hyperbolic space. We apply this to characterize hyperbolically embedded subgroups…

Group Theory · Mathematics 2012-10-31 Alessandro Sisto

In this paper, we study a special class of quasi-homomorphisms, i.e. quasi-retractions from a group to its subgroups. We first give some algebraic and geometric properties of quasi-retracts and then propose a theory of quasi-split short…

Group Theory · Mathematics 2025-08-21 Renxing Wan

We look for minimal conditions on a two-dimensional metric surface $X$ of locally finite Hausdorff $2$-measure under which $X$ admits an (almost) parametrization with good geometric and analytic properties. Only assuming that $X$ is locally…

Metric Geometry · Mathematics 2021-06-16 Damaris Meier , Stefan Wenger

In this paper we show that bending a finite volume hyperbolic $d$-manifold $M$ along a totally geodesic hypersurface $\Sigma$ results in a properly convex projective structure on $M$ with finite volume. We also discuss various geometric…

Geometric Topology · Mathematics 2020-04-10 Samuel A. Ballas , Ludovic Marquis

We study the group properties and the similarity solutions for the constraint conditions of anti-self-dual null K\"{a}hler four-dimensional manifolds with at least a Killing symmetry vector. Specifically we apply the theory of Lie…

General Relativity and Quantum Cosmology · Physics 2021-06-08 Andronikos Paliathanasis

We explore the combination theorem for a group G splitting as a graph of relatively hyperbolic groups. Using the fine graph approach to relative hyperbolicity, we find short proofs of the relative hyperbolicity of G under certain…

Group Theory · Mathematics 2012-11-14 Hadi Bigdely , Daniel T. Wise

We prove that the full automorphism group and the outer automorphism group of the free group of countably infinite rank are coarsely bounded. That is, these groups admit no continuous actions on a metric space with unbounded orbits, and…

Group Theory · Mathematics 2023-04-11 George Domat , Hannah Hoganson , Sanghoon Kwak

In the paper "Isoperimetry of waists and local versus global asymptotic convex geometries", it was proved that the existence of nicely bounded sections of two symmetric convex bodies K and L implies that the intersection of randomly rotated…

Functional Analysis · Mathematics 2016-12-23 Mark Rudelson , Roman Vershynin

A representation of a finitely generated group into the projective general linear group is called convex co-compact if it has finite kernel and its image acts convex co-compactly on a properly convex domain in real projective space. We…

Geometric Topology · Mathematics 2024-03-19 Mitul Islam , Andrew Zimmer

We prove combination theorems in the spirit of Klein and Maskit in the context of discrete convergence groups acting geometrically finitely on their limit sets. As special cases, we obtain combination theorems for geometrically finite…

Group Theory · Mathematics 2023-05-16 Alec Traaseth , Theodore Weisman

We develop the foundations of the theory of relatively geometric actions of relatively hyperbolic groups on CAT(0) cube complexes, a notion introduced in our previous work [5]. In the relatively geometric setting we prove: full relatively…

Group Theory · Mathematics 2022-03-09 Eduard Einstein , Daniel Groves

In this paper we study the local behavior of solutions to some free boundary problems. We relate the theory of quasi-conformal maps to the regularity of the solutions to nonlinear thin-obstacle problems; we prove that the contact set is…

Analysis of PDEs · Mathematics 2021-10-28 Guido De Philippis , Luca Spolaor , Bozhidar Velichkov

We study Bowditch's notion of a coarse median on a metric space and formally introduce the concept of a coarse median structure as an equivalence class of coarse medians up to closeness. We show that a group which possesses a uniformly…

Group Theory · Mathematics 2016-05-06 Rudolf Zeidler

In this paper, we prove a combination theorem for a relatively acylindrical graph of relatively hyperbolic groups (Theorem 1.1). Here, we are extending the technique of [Tom21] and constructing Bowditch boundary of the fundamental group of…

Group Theory · Mathematics 2022-07-08 Ravi Tomar