a1 Department of Mathematics, National University of Ireland, Galway, Ireland
a2 School of Mathematical Sciences, Dublin City University, Dublin 9, Ireland
We prove a generalisation of an observation of N. Iwahori concerning the coefficients of the extended Dynkin diagram of a complex simple Lie algebra. We relate the combinatorics of these coefficients to the orders of finite groups that act discontinuously on the Riemann sphere and to the Plücker formulae.
(Received January 27 2006)
(Revised September 27 2006)