Abstract
We give a positive answer, in the measurable-group-theory context, to von Neumann’s problem of knowing whether a non-amenable countable discrete group contains a non-cyclic free subgroup. We also get an embedding result of the free-group von Neumann factor into restricted wreath product factors.
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D. Gaboriau’s research was supported by CNRS.
R. Lyons’ research was supported partially by NSF grant DMS-0705518 and Microsoft Research.
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Gaboriau, D., Lyons, R. A measurable-group-theoretic solution to von Neumann’s problem. Invent. math. 177, 533–540 (2009). https://doi.org/10.1007/s00222-009-0187-5
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DOI: https://doi.org/10.1007/s00222-009-0187-5