Caltech-UCLA Logic Seminar
Friday, October 18, 2019
2:00pm to 3:30pmAdd to Cal
Quotients by countable subgroups are hyperfinite
Shinko Forte, Department of Mathematics, Caltech,
UCLA, MS 6221
Given a countable group Gamma, the outer automorphism group Out(Gamma) is either countable or of cardinality continuum. A finer and more suitable notion is to consider the Borel complexity of Out(Gamma) as a Borel equivalence relation. We show that in this context, Out(Gamma) is of rather low complexity, namely that it is a hyperfinite Borel equivalence relation. In general, we show that for any Polish group G and any countable normal subgroup Gamma, the quotient group G/Gamma is hyperfinite. This is joint work with Joshua Frisch.
For more information, please contact Math Department by phone at 626-395-4335 or by email at [email protected].
Event SeriesLogic Seminar Series