An equitable partition for a distance-regular graph of negative type

Let Γ denote a distance-regular graph with diameter d ⩾ 3 . Assume Γ has classical parameters ( d , b , α , β ) with b < - 1 . estigate the extent to which Γ is 1-homogeneous in the sense of Nomura. We show that either Γ is 1-homogeneous, or else Γ has a certain equitable partition of its vertex set which involves 4 d - 1 cells.