Cita APA (7a ed.)

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

Cita Chicago Style (17a ed.)

Appel, Kenneth I., y Wolfgang Haken. Every Planar Map Is Four Colorable. Providence, Rhode Island: American Mathematical Society, 1989.

Cita MLA (8a ed.)

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