On Faces of Quasi-arithmetic Coxeter Polytopes. (19th January 2021) - Bogachev, Nikolay
Abstract: We prove that each lower-dimensional face of a quasi-arithmetic Coxeter polytope, which happens to be itself a Coxeter polytope, is also quasi-arithmetic. We also provide a sufficient condition for a codimension $1$ face to be actually arithmetic, as well as a few computed examples. In memoriam È. B. Vinberg 1937–2020