Every 4-equivalenced association scheme is Frobenius

Abstract

For a positive integer $k$, we say that an association scheme $(\Omega,S)$ is $k$-equivalenced if each non-diagonal element of $S$ has valency $k$. $k$-equivalenced is weaker than pseudocyclic. It is known that every $k$-equivalenced association scheme is Frobenius when $k=2,3$ and every $4$-equivalenced association scheme is pseudocyclic. In this paper, we will show that every $4$-equivalenced association scheme is Frobenius.