1. Graph Theory: An Introductory Course, Number 63 in Graduate Texts in Mathematics;Bollobás,1990
2. Galois graphs: walks, trees and automorphisms;Brunat;J. Algeb. Combin.,1999
3. The characteristic ideal of a finite, connected, regular graph;Brunat,2004
4. C. Carathéodory, Theory of Functions of a Complex Variable, vol. 1, second ed., Chelsea Publishing Company, New York, 1983.
5. Graphs & Digraphs;Chartrand,1996