Mathematical Recreations; August 1997; Scientific American Magazine; by Stewart; 3 Page(s)

On the face of it, the Earthmoon problem is just a bit of harmless fun. Earth has been carved up into separate nations, each owning one connected region of territory--land and sea. Moreover, each earthly nation has annexed a region of the moon, to create an empire that consists of two pieces: one on Earth, the other on its satellite. What is the smallest number of colors that will cover any such map, so that both countries in any particular empire receive the same color but no two adjacent regions receive the same color--either on the moon or Earth?

The problem, which I first described in the April 1993 column, is highly artificial. A typically useless product of ivory tower intellectuals?