1. Biggs, N., Algebraic Graph Theory, Cambridge University Press 1974 (see Proposition 16.7, p. 110).
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3. Nosal, E., Eigenvalues of Graphs. Master thesis, University of Calgary, 1970.
4. Petersdorf, M. and Sachs, H., Spektrum und Automorphismengruppe eines Graphen. In: Combinatorial Theory and Its Applications, III. (eds. P. Erdős, A. Rényi and Vera T. Sós). North-Holland Publishing Company, Amsterdam-London 1970. pp. 891–907.
5. Sachs, H. and Stiebitz, M., Konstruktion schlichter transitiver Gruppen mit maximaler Anzahl einfacher Eigenwerte, Math. Nachr., 100 (1981), 145–150.