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Let $M$ be a finite von Neumann algebra (resp. a type II$_{1}$ factor) and let $N\subset M$ be a II$_{1}$ factor (resp. $N\subset M$ have an atomic part). We prove that the inclusion $N\subset M$ is amenable implies the identity map on $M$…

Operator Algebras · Mathematics 2018-09-05 Xiaoyan Zhou , Junsheng Fang

We show that an \'etale groupoid which is strongly amenable at infinity is amenable whenever its full and reduced $C^*$-algebras coincide.

Operator Algebras · Mathematics 2022-02-01 Julian Kranz

We introduce a wide class of countable groups, called properly proximal, which contains all non-amenable bi-exact groups, all non-elementary convergence groups, and all lattices in non-compact semi-simple Lie groups, but excludes all inner…

Operator Algebras · Mathematics 2018-11-15 Rémi Boutonnet , Adrian Ioana , Jesse Peterson

We investigate the isolated points in the space of finitely generated groups. We give a workable characterization of isolated groups and study their hereditary properties. Various examples of groups are shown to yield isolated groups. We…

Group Theory · Mathematics 2010-08-04 Yves de Cornulier , Luc Guyot , Wolfgang Pitsch

We show that a number of key structural properties transfer between sufficiently close II$_1$ factors, including solidity, strong solidity, uniqueness of Cartan masas and property $\Gamma$. We also examine II$_1$ factors close to tensor…

Operator Algebras · Mathematics 2016-06-01 Jan Cameron , Erik Christensen , Allan M. Sinclair , Roger R. Smith , Stuart White , Alan D. Wiggins

In this paper we introduce and study strongly singular maximal abelian self-adjoint subalgebras of type $II_1$ factors. We show that certain elements of free groups and of non-elementary hyperbolic groups generate such masas, and these also…

Operator Algebras · Mathematics 2016-09-07 Allan Sinclair , Roger Smith

We prove that the class of residually C groups is closed under taking graph products, provided that C is closed under taking subgroups, finite direct products and that free-by-C groups are residually C. As a consequence, we show that local…

Group Theory · Mathematics 2016-10-13 Federico Berlai , Michal Ferov

In this paper, we generalize Izumi's result on uniqueness of realization of finite C$^*$-tensor categories in the endomorphism category of the injective factor of type II_1 for finitely generated strongly amenable C$^*$-tensor categories by…

Operator Algebras · Mathematics 2016-11-03 Toshihiko Masuda

We consider various statements that characterize the hyperfinite II$_1$ factors amongst embeddable II$_1$ factors in the non-embeddable situation. In particular, we show that "generically" a II$_1$ factor has the Jung property (which states…

Operator Algebras · Mathematics 2021-01-27 Isaac Goldbring

We study II_1 factors M and N associated with good generalized Bernoulli actions of groups having an infinite almost normal subgroup with the relative property (T). We prove the following rigidity result: every finite index M-N-bimodule (in…

Operator Algebras · Mathematics 2009-01-20 Stefaan Vaes

We introduce the notions of definable amenability and extreme definable amenability for groups in continuous structures and conduct an extensive analysis of them, drawing parallels with the classical first-order case. We characterize both…

Logic · Mathematics 2025-04-03 Juan Felipe Carmona , Alf Onshuus

We construct a finitely presented (two-sided) totally orderable group with insoluble word problem.

Group Theory · Mathematics 2014-02-26 V. V. Bludov , A. M. W. Glass

We provide both a spectral and an internal characterizations of arbitrary I-favorable spaces with respect to co-zero sets. As a corollary we establish that any product of compact I-favorable spaces with respect to co-zero sets is also…

General Topology · Mathematics 2015-03-17 Vesko Valov

This is a continuation of our previous paper studying the structure of Cartan subalgebras of von Neumann factors of type II_1. We provide more examples of II_1 factors having either zero, one or several Cartan subalgebras. We also prove a…

Operator Algebras · Mathematics 2008-07-29 Narutaka Ozawa , Sorin Popa

We consider the group property of being icc. We give several examples of icc groups and study its stability under usual algebraic constructions.

Group Theory · Mathematics 2007-05-23 Jean-Philippe Preaux

We provide a family of group measure space II_1 factors for which all finite index subfactors can be explicitly listed. In particular, the set of all indices of irreducible subfactors can be computed. Concrete examples show that this index…

Operator Algebras · Mathematics 2011-11-29 Steven Deprez , Stefaan Vaes

Let $S$ be a subset of a amenable group $G$ such that $e\in S$ and $S^{-1}=S$. The main result of the paper states that if the Cayley graph of $G$ with respect to $S$ has a certain combinatorial property, then every positive definite…

Functional Analysis · Mathematics 2019-08-15 M. Bakonyi , D. Timotin

We show that the unitary group of any SOT-separable $\mathrm{II}_1$ factor $M$, with the strong operator topology, is contractible. Combined with several old results, this implies that the same is true for any SOT-separable von Neumann…

Operator Algebras · Mathematics 2025-09-04 David Jekel

A finitely generated solvable group with unbounded iterated identity is constructed.

Group Theory · Mathematics 2018-08-03 Roman Mikhailov

Uniformly finite homology is a coarse invariant for metric spaces; in particular, it is a quasi-isometry invariant for finitely generated groups. In this article, we study uniformly finite homology of finitely generated amenable groups and…

Group Theory · Mathematics 2016-01-20 Matthias Blank , Francesca Diana