On primitive commutative association schemes with a nonsymmetric relation of valency 4

Let (X, G) be a primitive commutative association scheme. If g is an elemen t of G is nonsymmetric of valency 4, then the graph (X, g) is uniquely dete rmined up to isomorphism. In particular, the cardinality of X is the cube o f an odd prime. (C) 1999 Academic Press.