T. De Medts, F. Haot, K. Tent, H. Van Maldeghem
July 27, 2005
Let ( G, B, N ) be a group with an irreducible spherical BN-pair of rank at least 2, and let U be a nilpotent normal subgroup of B such that B = U ( B ⋂ N ). We show that U is unique with respect to B . As a corollary, we obtain a complete classification of all irreducible spherical split BN-pairs of rank at least two.