Two New Characterizations of Path Graphs
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Path graphs are intersection graphs of paths in a tree. We start from the characterization of path graphs by Monma and Wei [C.L. Monma, and V.K. Wei, Intersection Graphs of Paths in a Tree, J. Combin. Theory Ser. B, 41:2 (1986) 141–181] and we reduce it to some 2-colorings subproblems, obtaining the first characterization that directly leads to a polynomial recognition algorithm. Then we introduce the collection of the attachedness graphs of a graph and we exhibit a list of minimal forbidden 2-edge colored subgraphs in each of the attachedness graph.
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