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A similar theorem states that K 4 and K 2,3 are the forbidden minors for the set of outerplanar graphs. Although the Robertson–Seymour theorem extends these results to arbitrary minor-closed graph families, it is not a complete substitute for these results, because it does not provide an explicit description of the obstruction set for any family.
Robertson, Seymour & Thomas (1993) proved the conjecture for =, also using the four color theorem; their paper with this proof won the 1994 Fulkerson Prize. It follows from their proof that linklessly embeddable graphs , a three-dimensional analogue of planar graphs, have chromatic number at most five. [ 3 ]
The Robertson–Seymour theorem proves that subcubic graphs (simple or not) are well-founded by homeomorphic embeddability, implying such a sequence cannot be infinite. Then, by applying KÅ‘nig's lemma on the tree of such sequences under extension, for each value of k there is a sequence with maximal length.
Robertson has won the Fulkerson Prize three times, in 1994 for his work on the Hadwiger conjecture, in 2006 for the Robertson–Seymour theorem, and in 2009 for his proof of the strong perfect graph theorem. [11] He also won the Pólya Prize (SIAM) in 2004, the OSU Distinguished Scholar Award in 1997, and the Waterloo Alumni Achievement Medal ...
The proof is based on a theorem of Robertson and Seymour that the families of graphs with unbounded treewidth have arbitrarily large grid minors. Seese also conjectured that every family of graphs with a decidable MSO 1 satisfiability problem must have bounded clique-width. [35]
As the Robertson–Seymour theorem shows, many important families of graphs can be characterized by a finite set of forbidden minors: for instance, according to Wagner's theorem, the planar graphs are exactly the graphs that have neither the complete graph K 5 nor the complete bipartite graph K 3,3 as minors.
Robertson–Seymour theorem; S. Schnyder's theorem; Sims conjecture; Steinitz's theorem; Strong perfect graph theorem; Symmetric hypergraph theorem; T. Turán's theorem;
In the first of their famous series of papers on graph minors, Neil Robertson and Paul Seymour define a path-decomposition of a graph G to be a sequence of subsets X i of vertices of G, with two properties: For each edge of G, there exists an i such that both endpoints of the edge belong to subset X i, and