Hikoe Enomoto Mirko Hornák Stanislav Jendrol Cyclic Chromatic Number of 3-Connected Plane Graphs. 121-137 2001 14 SIAM J. Discrete Math. 1 http://epubs.siam.org/sam-bin/dbq/article/34615 db/journals/siamdm/siamdm14.html#EnomotoHJ01