Take an outline map of the lower 48 U.S. states and four crayons. Can you shade in the map so that every state is a different color than each of its neighbors, without resorting to a fifth color? This ...

This was enough to prove the four color theorem, but getting there was not easy. The two mathematicians had to use a computer to check each one of the small maps to ensure it could indeed be ...

In mathematics, you need at most only four different colors to produce a map in which no two adjacent regions have the same color. Utah and Arizona are considered adjacent, but Utah and New Mexico ...