Solution of the heawood map-coloring problem—Cases 3, 5, 6, and 9

J.W.T. Youngs
1970 Journal of Combinatorial Theory  
This paper gives a proof of the fact that the chromatic number of an orientable surface of genus p is equal to the integral part of (7 + ~/1 + 48p)/2 whenever the latter is congruent to 3, 5, 6, or 9 modulo 12.
doi:10.1016/s0021-9800(70)80075-8 fatcat:l3hkhqzmlbcthasgfnf4imbtzm