  Let W be an irreducible finitely generated Coxeter group. The geometric
representation of W in GL(V) provides a discrete embedding in the orthogonal
group of the Tits form (the associated bilinear form of the Coxeter group). If
the Tits form of the Coxeter group is non-positive and non-degenerate, the
Coxeter group does not contain any finite index subgroup isomorphic to an
irreducible lattice in a semisimple group of R-rank greater or equal to 2.
