A CLASS OF ASSOCIATION SCHEMES IN WHICH ALL BASIS RELATIONS HAVE VALENCY 1 OR λ > 2

In this paper, we classify the commutative association schemes with both the property that each basis relation has valency either 1 or λ > 2 for some fixed λ and the property that there is a connected, symmetric basis relation R for which R2 contains exactly two basis relations. We show that up to isomorphism, the unique association scheme with these properties is the direct product of the trivial association scheme of order 2 and the trivial association scheme of order λ + 1.