Category Archives: seminar

Notes of Viktor Schroeder’s second informal Cambridge lecture 23-05-2017

Moebius structures on boundaries, II 1. Ptolemaic Moebius structures Recall that a Moebius structure is Ptolemaic if cross-ratios satisfy the Ptolemaic inequality, This means that takes its values in the triangle with vertices at the extra points . Examples Boundaries … Continue reading

Posted in seminar | Tagged | Leave a comment

Notes of Nicolas Matte Bon’s Cambridge lecture 23-05-2017

Uniformly recurrent subgroups and rigidity of non-free minimal actions Joint work with A. Le Boudec and T. Tsankov. 1. The Chabauty space of a group Let be a locally compact group. The Chabauty space of is the set of subgroups … Continue reading

Posted in seminar | Tagged | Leave a comment

Notes of Erik Guentner’s Cambridge lecture 23-05-2017

Affine actions, cohomology and hyperbolicity When can a group act properly on a Hilbert space or an space? I start from scratch. 1. Affine actions a discrete group, a Banach space. We are interested in actions of on where each … Continue reading

Posted in seminar | Tagged | Leave a comment

Notes of David Kyed’s Cambridge lecture 18-05-2017

-Betti numbers of universal quantum groups Joint with Pichon, Arndt, Vaes,… I spoke on the same subject in the same room in 2006. I think my understading has improved. 1. Infinite discrete groups Let act on vectorspace . There are … Continue reading

Posted in seminar | Tagged | Leave a comment

Notes of Nina Friedrich’s Cambridge lecture 17-05-2017

Homological stability of moduli spaces of high-dimensional manifolds 1. Manifolds Say a sequence manifolds and maps satisfies homological stability if induced maps on homomology groups become eventually isomorphisms. How does one prove such a property? We are interested in the … Continue reading

Posted in seminar | Tagged | Leave a comment

Notes of Viktor Schroeder’s first informal Cambridge lecture 16-05-2017

Moebius structures on boundaries, I This is an informal series of 3 lectures. I start with boundaries of hyperbolic groups. I will continue with Furstenberg boundaries of higher rank symmetric spaces (joint work with my student Beyrer). 1. Moebius structures … Continue reading

Posted in seminar | Tagged | Leave a comment

Notes of Yves Cornulier’s Cambridge lecture 16-05-2017

Commensurating actions of groups of birational transformations Joint work with Serge Cantat. 1. Birational geometry This is more than a century old. Let be irreducible varieties over . A rational map is a regular (given by the ratio of two … Continue reading

Posted in seminar | Tagged | Leave a comment