Connectivity and tree structure in finite graphs

Abstract

Considering systems of separations in a graph that separate every pair of a given set of vertex sets that are themselves not separated by these separations, we determine conditionsunder which such a separation system contains a nested subsystem that still separates those sets and is invariant under the automorphisms of the graph.

As an application, we show that the k-blocks — the maximal vertex sets that cannot be separated by at most k vertices — of a graph G live in distinct parts of a suitable treedecomposition of G of adhesion at most k, whose decomposition tree is invariant under the automorphisms of G. This extends recent work of Dunwoody and Krön and, like theirs, generalizes a similar theorem of Tutte for k=2.

Under mild additional assumptions, which are necessary, our decompositions can be combined into one overall tree-decomposition that distinguishes, for all k simultaneously, all the k-blocks of a finite graph.

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Correspondence to Reinhard Diestel.

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Supported by Fondecyt grant no 11090141

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Carmesin, J., Diestel, R., Hundertmark, F. et al. Connectivity and tree structure in finite graphs. Combinatorica 34, 11–46 (2014). https://doi.org/10.1007/s00493-014-2898-5

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Mathematics Subject Classification (2000)

  • 05C40
  • 05C05
  • 05C83