References
Diestel, Reinhard., Graph Theory. Springer, 2000.
Chiba, N., Nishizeki, T., Saito, N., A Linear Algorithm For Five-Coloring A Planar Graph. Lecture Notes in Computer Science: Graph Theory and Algorithms, 1980 Proceedings, Springer-Verlag.
Read, Ronald C., Graph Theory and Computing. Academic Press, New York, 1972.