Some of the things I've learned every day since Oct 10, 2016
61: Coloring Problem on the Torus
December 11, 2016Posted by on
Given any division of a (2-)torus into regions, it is possible to color the regions with 7 distinct colors so that no two adjacent regions have the same color.
This contrasts with the more well-known fact that the plane is 4-colorable.