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Diagonal actions and Borel equivalence relations
Published online by Cambridge University Press: 12 March 2014
Abstract
We investigate diagonal actions of Polish groups and the related intersection operator on closed subgroups of the acting group. The Borelness of the diagonal orbit equivalence relation is characterized and is shown to be connected with the Borelness of the intersection operator. We also consider relatively tame Polish groups and give a characterization of them in the class of countable products of countable abelian groups. Finally an example of a logic action is considered and its complexity in the Borel reducbility hierarchy determined.
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- Copyright © Association for Symbolic Logic 2006
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