1. Algebraic Combinatorics I, Association Schemes;Bannai,1984
2. The theory of non-symmetric association schemes with three classes;Claasen,1986
3. An algebraic approach to the association schemes of coding theory;Delsarte;Philips Research Report Supplements,1973
4. Distance-regular digraphs of girth 4;Enomoto;J. Combin. Theory, Ser. B,1987