Groups, Geometry, and Dynamics


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Volume 2, Issue 2, 2008, pp. 139–163
DOI: 10.4171/GGD/34

Published online: 2008-06-30

Minimal topological actions do not determine the measurable orbit equivalence class

Tullio Ceccherini-Silberstein[1] and Gábor Elek[2]

(1) Università del Sannio, Benevento, Italy
(2) Hungarian Academy of Sciences, Budapest, Hungary

We construct an amenable action Φ of a non-amenable group Γ on a discrete space. This action extends to a minimal topological action Φ of Γ on a Cantor set C. We show that Φ is non-uniquely ergodic and furthermore there exist ergodic invariant measures μ1 and μ2 such that (Φ,C,μ1) and (Φ,C,μ2) are not orbit equivalent measurable equivalence relations. This also provides an instance of the failure of equivalence between the notions of “global” and “local” amenability for countable equivalence relations.

Keywords: Minimal actions, measurable equivalence relations, orbit equivalence, amenable actions, amenable graphs, hyperfiniteness

Ceccherini-Silberstein Tullio, Elek Gábor: Minimal topological actions do not determine the measurable orbit equivalence class. Groups Geom. Dyn. 2 (2008), 139-163. doi: 10.4171/GGD/34