Suzuki (1998)  showed that an imprimitive Q-polynomial association scheme with first multiplicity at least 3 is Q-bipartite, or is Q-antipodal, or has four or six classes. The exceptional case with four classes has recently been ruled out by Cerzo and Suzuki (2009) . In this paper, we show the nonexistence of the last case with six classes. Hence Suzuki's theorem now exactly mirrors its well-known counterpart for imprimitive distance-regular graphs.
ASJC Scopus subject areas
- Discrete Mathematics and Combinatorics