APA (7th ed.) Citation

Ore, O. (1967). The four-color problem (2. print.). Acad. Press.

Chicago Style (17th ed.) Citation

Ore, Oystein. The Four-color Problem. 2. print. New York [u.a.]: Acad. Press, 1967.

MLA (9th ed.) Citation

Ore, Oystein. The Four-color Problem. 2. print. Acad. Press, 1967.