Universal Borel actions of countable groups

  • Simon Thomas

    Rutgers University, Piscataway, United States


If the countable group GG has a nonabelian free subgroup, then there exists a standard Borel GG-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.

Cite this article

Simon Thomas, Universal Borel actions of countable groups. Groups Geom. Dyn. 6 (2012), no. 2, pp. 389–407

DOI 10.4171/GGD/161