Let (X, {R-i} (0) (less than or equal to) (i) (less than or equal to) (d))
be a primitive commutative association scheme. If there is a non-symmetric
relation R-i with valency 3, then the cardinality of X is equal to either p
or p(2) where p is an odd prime. Moreover, if \X\ = p then (X, {R-i} (0) (
less than or equal to) (i) (less than or equal to d)) is isomorphic to a cy
clotomic scheme. (C) 2000 Academic Press.