Cita APA

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

Citación estilo Chicago

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

Cita MLA

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