APA (7th ed.) Citation

Ore, O. (1967). The four-color problem / by O. Ore. Academic.

Chicago Style (17th ed.) Citation

Ore, Oystein. The Four-color Problem / by O. Ore. Academic, 1967.

MLA (9th ed.) Citation

Ore, Oystein. The Four-color Problem / by O. Ore. Academic, 1967.

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