Arboricity and tree-packing in locally finite graphs

  • Authors:
  • Maya Jakobine Stein

  • Affiliations:
  • Mathematisches Seminar, Universität Hamburg, Bundesstraße 55, 20146 Hamburg, Germany

  • Venue:
  • Journal of Combinatorial Theory Series B
  • Year:
  • 2006

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Abstract

Nash-Williams' arboricity theorem states that a finite graph is the edge-disjoint union of at most k forests if no set of @? vertices induces more than k(@?-1) edges. We prove a natural topological extension of this for locally finite infinite graphs, in which the partitioning forests are acyclic in the stronger sense that their Freudenthal compactification-the space obtained by adding their ends-contains no homeomorphic image of S^1. The strengthening we prove, which requires an upper bound on the end degrees of the graph, confirms a conjecture of Diestel [The cycle space of an infinite graph, Combin. Probab. Comput. 14 (2005) 59-79]. We further prove for locally finite graphs a topological version of the tree-packing theorem of Nash-Williams and Tutte.