Bar-Ilan Algebra Seminar ========================================= Date: Wednesday, 14 Iyar 5771 // May 18, 2011 Time: 10:00 am promptly PLEASE NOTE THE CHANGE OF TIME Place: Third floor seminar room, Mathematics building Speaker: Prof. Daniel Lenz (Friedrich-Schiller-Universitaet Jena) Title: Order based constructions of groupoids from inverse semigroups Abstract: We discuss how the universal groupoid of an inverse semigroup introduced by Paterson can be obtained by a simple order based construction. Along the way one obtains canonically a reduction of this groupoid. In the case of inverse semigroups arising from graphs (respectively, tilings) this reduction is the graph groupoid introduced by Kumjian et al. (respectively, the tiling groupoid of Kellendonk). We discuss some topological features of this reduction as well as the structure of its open invariant sets. This can be used to investigate the ideal structure of an associated reduced $C^*t$-algebra. --------------------------------------------------------- Technion Math Net-2 (TECHMATH2) Editor: Michael Cwikel <techm@math.technion.ac.il> Announcement from: Michael Schein <mschein@math.biu.ac.il>