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  2. Robertson–Seymour theorem - Wikipedia

    en.wikipedia.org/wiki/RobertsonSeymour_theorem

    A similar theorem states that K 4 and K 2,3 are the forbidden minors for the set of outerplanar graphs. Although the RobertsonSeymour 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.

  3. Graph minor - Wikipedia

    en.wikipedia.org/wiki/Graph_minor

    An edge contraction is an operation that removes an edge from a graph while simultaneously merging the two vertices it used to connect. An undirected graph H is a minor of another undirected graph G if a graph isomorphic to H can be obtained from G by contracting some edges, deleting some edges, and deleting some isolated vertices.

  4. Pathwidth - Wikipedia

    en.wikipedia.org/wiki/Pathwidth

    In the language of the later papers in Robertson and Seymour's graph minor series, a path-decomposition is a tree decomposition (X,T) in which the underlying tree T of the decomposition is a path graph.

  5. Graph structure theorem - Wikipedia

    en.wikipedia.org/wiki/Graph_structure_theorem

    A minor of a graph G is any graph H that is isomorphic to a graph that can be obtained from a subgraph of G by contracting some edges. If G does not have a graph H as a minor, then we say that G is H-free. Let H be a fixed graph. Intuitively, if G is a huge H-free graph, then there ought to be a "good reason" for this.

  6. Graph minors theorem - Wikipedia

    en.wikipedia.org/?title=Graph_minors_theorem&...

    Retrieved from "https://en.wikipedia.org/w/index.php?title=Graph_minors_theorem&oldid=1102375387"

  7. Neil Robertson (mathematician) - Wikipedia

    en.wikipedia.org/wiki/Neil_Robertson_(mathematician)

    In 1993, with Seymour and Robin Thomas, Robertson proved the -free case for which the Hadwiger conjecture relating graph coloring to graph minors is known to be true. [ 8 ] In 1996, Robertson, Seymour, Thomas, and Daniel P. Sanders published a new proof of the four color theorem , [ 9 ] confirming the Appel–Haken proof which until then had ...

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  9. Petersen family - Wikipedia

    en.wikipedia.org/wiki/Petersen_family

    Each of the Petersen family graphs forms a minimal forbidden minor for the family of YΔY-reducible graphs. [2] However, Neil Robertson provided an example of an apex graph (a linkless embeddable graph formed by adding one vertex to a planar graph) that is not YΔY-reducible, showing that the YΔY-reducible graphs form a proper subclass of the ...

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