Series: Penn State Logic Seminar

Date: Wednesday, June 30, 2004

Time: 11:10 AM - 12:25 PM

Place: 311 Boucke Building

Speaker: John Clemens, Penn State, Mathematics

Title: Turbulence, part 3 of 3
        
Abstract:

  A definable equivalence relation is said to be Classifiable by
  Countable Structures if there is a Borel way of assigning
  isomorphism types of countable structures as complete
  invariants. This is a useful benchmark for gauging the complexity of
  many equivalence relations. Hjorth's theory of Turbulence provides a
  powerful technique for showing that certain equivalence relations
  are not classifiable by countable structures. I will present the
  definition of a turbulent group action and the proof that such
  actions are not classifiable by countable structures. I will then
  discuss some applications of this theory to specific equivalence
  relations of interest.