APA (7th ed.) Citation

Ore, O. (1967). The four-colour problem. Academic Press.

Chicago Style (17th ed.) Citation

Ore, Oystein. The Four-colour Problem. Nueva York: Academic Press, 1967.

MLA (9th ed.) Citation

Ore, Oystein. The Four-colour Problem. Academic Press, 1967.

Warning: These citations may not always be 100% accurate.