Four color map theorem
From MysteryWiki
References
- Appel, K., and W. Haken. "Every Planar Map Is Four Colorable. Part I: Discharging." Illinois Journal of Mathematics 23.3 (1977): 429-90. Print.
- Franklin, Philip. "The Four Color Problem." American Journal of Mathematics 44.3 (1922): 225-36. Print.