APA (7th ed.) Citation

Appel, K. I., & Haken, W. (1989). Every planar map is four colorable. American Mathematical Society.

Chicago Style (17th ed.) Citation

Appel, Kenneth I., and Wolfgang Haken. Every Planar Map Is Four Colorable. Providence, RI: American Mathematical Society, 1989.

MLA (9th ed.) Citation

Appel, Kenneth I., and Wolfgang Haken. Every Planar Map Is Four Colorable. American Mathematical Society, 1989.