Citazione Stile APA (7a Edizione)

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

Citazione stile Chigago Style (17a edizione)

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

Citatione MLA (9a ed.)

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