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Some cases of polynomial solvability of the edge coloring problem that are generated by forbidden 8-edge subcubic forests
The edge-coloring problem is to minimize the number of colors sufficient to color all the edges of a given graph so that any adjacent edges receive distinct colors. The complexity status of this problem is known for all the classes defined by the sets of forbidden subgraphs with 7 edges each. In this paper, we consider the case of prohibitions with 8 edges. It can readily be seen that the edge-coloring problem is NP-complete for such a class if there are no subcubic forests among its 8-edge prohibitions. We prove that forbidding any subcubic 8-edge forest generates a class with polynomial-time solvability of the edge-coloring problem, except for the cases formed by the disjoint sum of one of four forests and an empty graph. For all the remaining cases, we prove a similar result for the intersection with the set of graphs with a maximum degree of at least four.