Title: Reflection groups beyond Coxeter groups.
Abstract: All Coxeter groups are reflection groups. And there are many contexts where "reflection group" and "Coxeter group" mean essentially the same thing. In this talk I will
highlight a case where these notions are different. Concretely, a discrete group generated by finitely many reflections preserving a non-singular quadratic form on a real metric vector space
need not be a Coxeter group.


