Fritsch, R., & Fritsch Gerda. (1998). Four colour theorem.
Chicago Edition CitationFritsch, Rudolf, and Fritsch Gerda. Four Colour Theorem. Springer-Verlag, New York, 1998.
MLA Edition CitationFritsch, Rudolf, and Fritsch Gerda. Four Colour Theorem. 1998.
Warning: These citations may not always be 100% accurate.