APA (7th ed.) Citation

Appel, K. I. (1989). Every planar map is four colorable. American Mathematical Society. https://doi.org/10.1090/conm/098

Chicago Style (17th ed.) Citation

Appel, Kenneth I. Every Planar Map Is Four Colorable. Providence, R.I: American Mathematical Society, 1989. https://doi.org/10.1090/conm/098.

MLA (9th ed.) Citation

Appel, Kenneth I. Every Planar Map Is Four Colorable. American Mathematical Society, 1989. https://doi.org/10.1090/conm/098.