English

Edmonds' Branching Theorem in Digraphs without Forward-infinite Paths

Combinatorics 2017-05-02 v1

Abstract

Let D D be a finite digraph, and let V0,,Vk1 V_0,\dots,V_{k-1} be nonempty subsets of V(D) V(D) . The (strong form of) Edmonds' branching theorem states thatthere are pairwise edge-disjoint spanning branchings B0,,Bk1 \mathcal{B}_0,\dots, \mathcal{B}_{k-1} in D D such that the root set of Bi \mathcal{B}_i is Vi (i=0,,k1) V_i\ (i=0,\dots,k-1) if and only if for all XV(D) \varnothing \neq X\subseteq V(D) the number of ingoing edges of X X is greater than or equal to the number of sets Vi V_i disjoint from X X . As was shown by R. Aharoni and C. Thomassen in \cite{aharoni1989infinite}, this theorem does not remain true for infinite digraphs. Thomassen also proved that for the class of digraphs without backward-infinite paths, the above theorem of Edmonds remains true. Our main result is that for digraphs without forward-infinite paths, Edmonds' branching theorem remains true as well.

Keywords

Cite

@article{arxiv.1705.00471,
  title  = {Edmonds' Branching Theorem in Digraphs without Forward-infinite Paths},
  author = {Attila Joó},
  journal= {arXiv preprint arXiv:1705.00471},
  year   = {2017}
}
R2 v1 2026-06-22T19:32:38.346Z