In 1852, Francis Guthrie was discussing with his brother Frederick the coloring of a map. He discovered the fact that he could color the map of England counties with the use of only four colors. He used the colors in such a way that each division had a single color and two segments sharing a common boundary had different colors. Thus, the four color problem was born and the question arose whether in a plane map, four colors were sufficient to denote the divisions of adjacent regions sharing the same boundary, without using the same colors.
A.B. Kempe is ...