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Von Neumann equivalence and properly proximal groups Ruth, Lauren


We introduce a new equivalence relation on groups, which we call von Neumann equivalence, and which is coarser than both measure equivalence and W*-equivalnce. We introduce a general procedure for inducing actions in this setting and use this to show that the class of properly proximal groups is closed in this equivalence relation. In particular, proper proximality is preserved under both measure equivalence and W*-equivalence, and from this we obtain examples of non-inner amenable groups which are not properly proximal. This is based on joint work with Ishan Ishan and Jesse Peterson.

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