APA (7th ed.) Citation

Ore, Ø. (1967). The four-color problem. Academic Press.

Chicago Style (17th ed.) Citation

Ore, Øystein. The Four-color Problem. New York, NY [u.a.]: Academic Press, 1967.

MLA (9th ed.) Citation

Ore, Øystein. The Four-color Problem. Academic Press, 1967.