English

Enlarging vertex-flames in countable digraphs

Combinatorics 2021-06-17 v2

Abstract

A rooted digraph is a vertex-flame if for every vertex vv there is a set of internally disjoint directed paths from the root to vv whose set of terminal edges covers all ingoing edges of vv. It was shown by Lov\'{a}sz that every finite rooted digraph admits a spanning subdigraph which is a vertex-flame and large, where the latter means that it preserves the local connectivity to each vertex from the root. A structural generalisation of vertex-flames and largeness to infinite digraphs was given by the third author and the analogue of Lov\'{a}sz' result for countable digraphs was shown. We strengthen this result by proving that in every countable rooted digraph each vertex-flame can be extended to a large vertex-flame.

Keywords

Cite

@article{arxiv.2003.06178,
  title  = {Enlarging vertex-flames in countable digraphs},
  author = {Joshua Erde and J. Pascal Gollin and Attila Joó},
  journal= {arXiv preprint arXiv:2003.06178},
  year   = {2021}
}
R2 v1 2026-06-23T14:13:43.650Z