UPDATE: the room is now Carslaw 157, not 173. There will be a Group Actions Seminar at the University of Sydney next week, on Monday 24 June. The speakers will be Pallavi Dani (Louisiana State) and Giles Gardam (Sydney). Titles and abstracts are below. ---------------------------------------------------------------------------- Date: Monday 24 June Time: 12 noon Location: Carslaw 157, University of Sydney Speaker: Pallavi Dani (Louisiana State University) Title: Filling invariants: homological vs. homotopical Abstract: Classical isoperimetric functions give optimal bounds on the minimal-area fillings of loops by disks. There are a number of variations: rather than sticking to loops and disks, one might consider fillings of spheres by balls, or cycles by chains. A natural question then is: for a given space are these functions the same? Or are there spaces in which a particular type of filling (say filling cycles by chains) is more efficient than other types? What if the space is quasi-isometric to a finitely presented group? I will talk about recent work with A. Abrams, N. Brady and R. Young which addresses this question. ---------------------------------------------------------------- Date: Monday 24 June Time: 3pm Location: Carslaw 157, University of Sydney Speaker: Giles Gardam (University of Sydney) Title: Graphs and triangles of groups Abstract: Bass-Serre theory studies group actions on trees, unifying two combinatorial constructions from group theory, namely free product with amalgamation and the HNN extension, which are understood as special cases of graphs of groups. This talk will give an introduction to Bass-Serre theory up to and including its so-called fundamental theorem. We will also introduce Gersten and Stallings’ notion of non-positively curved triangles of groups, as a first step towards the more general theory of complexes of groups. ----------------------------------------------------------------