14.00 - 14.45 : François Thilmany (KU Leuven) « Finding ping-pong partners for finite subgroups of linear groups » In his paper on free subgroups of linear groups, Tits proved his famous alternative: a linear group is either virtually solvable, or contains a free subgroup. Since then, Tits’ work has been generalized and applied in many different ways. One remaining open question in this subject is the one asked by de la Harpe and his collaborators: let $G$ be a semisimple Lie group without compact factors and with trivial center, and let $\Gamma$ […]