Logic Seminar
Dave Marker
UIC
Borel complexity of isomorphism for theories with many types
Abstract: If E is a Borel equivalence relation with countably many classes, then there is an infinitary sentence $\phi$
such that E is Borel bi-reducible to the isomorphism relation for $\phi$. Kechris and Hjorth asked if the
same was true for first order theories. We show that if a theory has uncountably many types, then the
isomorphism relation is more complicated than any Borel equivalence relation with countably many
classes.
Tuesday September 5, 2006 at 4:00 PM in SEO 427