File:7x-torus.svg

A partition of the torus into seven mutually adjacent regions, requiring seven colors. The torus is shown unrolled onto a square; points on the top edge of the square should be thought of as connected to the corresponding points on the bottom edge of the square, and points on the left edge of the square should be thought of as connected to the corresponding points on the right edge of the square. The edges and vertices of the regions form an embedding of the en:Heawood graph onto the torus. A combinatorially equivalent partition of the torus into regions forms the set of faces of the en:Szilassi polyhedron.