Weyl groups of some hyperbolic Kac-Moody algebras
  We use the theory of Clifford algebras and Vahlen groups to study Weyl groups of hyperbolic Kac-Moody algebras T_n^{++}, obtained by a process of double extension from a Cartan matrix of finite type T_n, whose corresponding generalized Cartan matrices are symmetric. 
Alex J. Feingold and Daniel Valli\`eres
math.GR math.RA math.RT