Incidence Coloring—Cold Cases
Discussiones Mathematicae. Graph Theory, Tome 40 (2020) no. 1, pp. 345-354

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An incidence in a graph G is a pair (v, e) where v is a vertex of G and e is an edge of G incident to v. Two incidences (v, e) and (u, f) are adjacent if at least one of the following holds: (i) v = u, (ii) e = f, or (iii) edge vu is from the set e, f. An incidence coloring of G is a coloring of its incidences assigning distinct colors to adjacent incidences. The minimum number of colors needed for incidence coloring of a graph is called the incidence chromatic number. It was proved that at most Δ(G) + 5 colors are enough for an incidence coloring of any planar graph G except for Δ(G) = 6, in which case at most 12 colors are needed. It is also known that every planar graph G with girth at least 6 and Δ(G) ≥ 5 has incidence chromatic number at most Δ(G) + 2. In this paper we present some results on graphs regarding their maximum degree and maximum average degree. We improve the bound for planar graphs with Δ(G) = 6. We show that the incidence chromatic number is at most Δ(G) + 2 for any graph G with mad(G) lt; 3 and Δ(G) = 4, and for any graph with mad(G) lt;103 and Δ(G) ≥ 8.
Keywords: incidence coloring, incidence chromatic number, planar graph, maximum average degree
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Kardoš, František; Maceková, Mária; Mockovčiaková, Martina; Sopena, Éric; Soták, Roman. Incidence Coloring—Cold Cases. Discussiones Mathematicae. Graph Theory, Tome 40 (2020) no. 1, pp. 345-354. http://geodesic.mathdoc.fr/item/DMGT_2020_40_1_a23/