Cita APA (7th ed.)

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

Cita Chicago (17th ed.)

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

Cita MLA (9th ed.)

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