Groups, Geometry, and Dynamics
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Published online: 2012-04-16
Universal Borel actions of countable groupsSimon Thomas (1) Rutgers University, Piscataway, United States
If the countable group $G$ has a nonabelian free subgroup, then there exists a standard Borel $G$-space such that the corresponding orbit equivalence relation is countable universal. In this paper, we will consider the question of whether the converse also holds.
Keywords: Borel equivalence relation, superrigidity, sofic groups
Thomas Simon: Universal Borel actions of countable groups. Groups Geom. Dyn. 6 (2012), 389-407. doi: 10.4171/GGD/161