1. Cvetkovic, D.M., Doob, M., Sachs, H.: Spectra of Graphs. London: Academic Press 1980
2. Geramita, A.V., Seberry, J.: Orthogonal Designs. Marcel Dekker 1979
3. Ito, N.: Doubly regular asymmetric digraphs. Discrete Math.72, 181–185 (1988)
4. Ito, N.: Automorphism groups of DRADs. In: Proc. of Group Theory Conference 1987 Singapore 151–170 (1989)
5. Ito, N., Nakamori, Y., Umayahara, K.: Doubly regular asymmetric (16, 6, 2) digraphs. Memoirs of Konan University34, 173–198 (1987)