A proper edge coloring f of a graph G with colors 1, 2, 3, . . . , t is called an interval coloring if the colors on the edges incident to every vertex of G form an interval of integers. The coloring f is cyclic interval if for every vertex v of G, the colors on the edges incident to v either form an interval or the set {1, . . . t} \ {f (e) : e is incident to v} is an interval. A bipartite graph G is (a, b)-biregular if every vertex in one part has degree a and every vertex in the other part has degree b; it has been conjectured that all such graphs have interval colorings. We prove that every (3, 5)-biregular graph has a cyclic interval coloring and we give several sufficient conditions for a (3, 5)-biregular graph to admit an interval coloring. (C) 2016 Elsevier B.V. All rights reserved.
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