H. Broersma, F. V. Fomin, P. A. Golovach, and G. J. Woeginger, Backbone colorings for graphs: Tree and path backbones, Journal of Graph Theory, vol.94, issue.2, pp.137-152, 2007.
DOI : 10.1002/jgt.20228

K. Appel and W. Haken, Every planar map is four colorable, Bulletin of Americain mathematical society 82

F. Havet, A. D. King, M. Liedloff, and I. Todinca, (Circular) backbone colouring: Forest backbones in planar graphs, Discrete Applied Mathematics, vol.169, pp.119-134, 2014.
DOI : 10.1016/j.dam.2014.01.011

URL : https://hal.archives-ouvertes.fr/hal-00957243

V. Campos, F. Havet, R. Sampaio, and A. Silva, Backbone colouring: Tree backbones with small diameter in planar graphs, Theoretical Computer Science, vol.487, issue.0, pp.50-64, 2013.
DOI : 10.1016/j.tcs.2013.03.003

URL : https://hal.archives-ouvertes.fr/hal-00758548

H. Grötzsch, Zur Theorie der diskreten Gebilde. VII. Ein Dreifarbensatz für dreikreisfreie Netze auf der Kugel, Wiss. Z. Martin-Luther-Univ. Halle- Wittenberg. Math.-Nat. Reihe, vol.8, pp.109-120, 1958.

R. Steinberg, The State of the Three Color Problem, Ann. Discrete Math, vol.55, issue.08, pp.211-248, 1993.
DOI : 10.1016/S0167-5060(08)70391-1