Fritsch, R., & Fritsch, G. (1998). The four color theorem: History, topological foundations, and idea of proof. Springer.
Dyfyniad Arddull ChicagoFritsch, Rudolf, and Gerda Fritsch. The Four Color Theorem: History, Topological Foundations, and Idea of Proof. New York: Springer, 1998.
Dyfyniad MLAFritsch, Rudolf, and Gerda Fritsch. The Four Color Theorem: History, Topological Foundations, and Idea of Proof. Springer, 1998.
Rhybudd: Mae'n bosib nad yw'r dyfyniadau hyn bob amser yn 100% cywir.