Thursday, September 29, 4:00-5:30, East Hall 3096.
An equivalence relation E is hypersmooth (hyperfinite) if E is the union of an increasing sequence of smooth (finite) Borel equivalence relations. In the mid 80s, Weiss proved that the equivalence relation generated by a finite family of commuting Borel automorphisms is hyperfinite, and in the mid 90s, Dougherty, Jackson, and Kechris proved that the equivalence relation generated by a single Borel endomorphism is hypersmooth. We will generalize both results to show that the equivalence relation generated by a finite family of commuting Borel endomorphisms is hypersmooth. As is typical in this area, the proof will involve the construction of a suitable family of Borel marker sets. This is the second of a series of talks.