Visit of professor Uli Wagner

September 2015 : Three one-month visits of Professor Uli Wagner (Institute of Science and Technology, Austria) are supported by the Labex Bezout for 2014-2016. During the first visit, in september 2014, Uli Wagner gave a talk in the probability seminar (LAMA) on higher-dimensional expanders (which served as an outlook of a serie of technical talks on expanders that unfolded later in the semester) and another one in the discrete geometry seminar at IHP. He also initiated a work with Xavier Goaoc (LIGM) on an approximate version of the Nerve theorem in algebraic topology.