Graph minors XXIII. Nash-Williams' immersion conjecture

  • Authors:
  • Neil Robertson;Paul Seymour

  • Affiliations:
  • Ohio State University, Columbus, OH, United States;Princeton University, Princeton, NJ, United States

  • Venue:
  • Journal of Combinatorial Theory Series B
  • Year:
  • 2010

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Abstract

We define a quasi-order of the class of all finite hypergraphs, and prove it is a well-quasi-order. This has two corollaries of interest:*Wagner's conjecture, proved in a previous paper, states that for every infinite set of finite graphs, one of its members is a minor of another. The present result implies the same conclusion even if the vertices or edges of the graphs are labelled from a well-quasi-order and we require the minor relation to respect the labels. *Nash-Williams' ''immersion'' conjecture states that in any infinite set of finite graphs, one can be ''immersed'' in another; roughly, embedded such that the edges of the first graph are represented by edge-disjoint paths of the second. The present result implies this, in a strengthened form where we permit vertices to be labelled from a well-quasi-order and require the immersion to respect the labels.