Six-Color Theorem

To color any map on the Sphere or the Plane requires at most six-colors. This number can easily be reduced to five, and the Four-Color Theorem demonstrates that the Necessary number is, in fact, four.

See also Four-Color Theorem, Heawood Conjecture, Map Coloring

References

Franklin, P. ``A Six Colour Problem.'' J. Math. Phys. 13, 363-369, 1934.

Hoffman, I. and Soifer, A. ``Another Six-Coloring of the Plane.'' Disc. Math. 150, 427-429, 1996.

Saaty, T. L. and Kainen, P. C. The Four-Color Problem: Assaults and Conquest. New York: Dover, 1986.