The unbalanced graph of the conjugacy relation of ergodic measure-preserving transformations

Abstract

We show that the isomorphism of ergodic measure-preserving transformations is not Borel reducible to the relation induced by the conjugacy action of the full group of an ergodic measure-preserving transformation on itself. This answers a question of Le Maître in the negative and gives a positive indication towards a conjecture of Sabok. On the other hand, we prove that the conjugacy relation of ergodic measure-preserving transformations is not unbalanced, which answers another question of Le Maître in the negative. On the positive side, we prove that every two ergodic measure-preserving transformations are connected by a path of length two in the unbalanced graph on the set of ergodic measure-preserving transformations.

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