# Events for 06/24/2020 from all calendars

## Groups and Dynamics Seminar

Time: 12:00PM - 1:00PM

Location: 940 9667 3668

Speaker: Nicolás Matte Bon, ETH Zürich

Title: A commutator lemma for confined subgroups and URS's and application to groups acting on rooted trees.

Abstract: I will explain a commutator lemma for confined subgroups and URSs of a group of homeomorphism, which generalizes to this setting a well-known lemma that relates normal subgroups of a group of homeomorphisms to the rigid stabilizers of the open sets of its action. Then we will focus on various application to weakly branch groups acting on rooted trees.

## Noncommutative Geometry Seminar

Time: 1:00PM - 2:00PM

Location: Zoom 942810031

Speaker: Carla Farsi, University of Colorado - Boulder

Title: Proper Lie Groupoids and their structures

Abstract: I will talk about two projects in their final phase of completion. (Joint with Scull and Watts) After defining the orbit category for transitive proper Lie groupoids and equivariant CW-complexes, we define equivariant Bredon homology and cohomology theories for actions of transitive proper Lie groupoids by using similarities with the compact group action case. Our work can be seen as basic evidence for Morita equivalence invariance of general Bredon theories. (Joint with Seaton) After defining groupoid Euler characteristics for cocompact proper Lie groupoids we prove that they can be realized as the usual Euler characteristic of groupoid inertias spaces. We prove that these Euler Characteristics are Morita invariant and extend those defined for orbifolds and G-spaces where G is a compact Lie group.