Frédéric Havet Jean-Sébastien Sereni Riste Skrekovski 3-Facial Coloring of Plane Graphs. 231-247 2008 22 SIAM J. Discrete Math. 1 http://dx.doi.org/10.1137/060664124 db/journals/siamdm/siamdm22.html#HavetSS08