English

The Erd\H{o}s-P\'osa property for infinite graphs

Combinatorics 2024-11-06 v1

Abstract

We investigate which classes of infinite graphs have the Erd\H{o}s-P\'osa property (EPP). In addition to the usual EPP, we also consider the following infinite variant of the EPP: a class G\mathcal{G} of graphs has the κ\kappa-EPP, where κ\kappa is an infinite cardinal, if for any graph Γ\Gamma there are either κ\kappa disjoint graphs from G\mathcal{G} in Γ\Gamma or there is a set XX of vertices of Γ\Gamma of size less than κ\kappa such that ΓX\Gamma - X contains no graph from G\mathcal{G}. In particular, we study the (κ\kappa-)EPP for classes consisting of a single infinite graph GG. We obtain positive results when the set of induced subgraphs of GG is labelled well-quasi-ordered, and negative results when GG is not a proper subgraph of itself (both results require some additional conditions). As a corollary, we obtain that every graph which does not contain a path of length nn for some nNn \in \mathbb{N} has the EPP and the κ\kappa-EPP. Furthermore, we show that the class of all subdivisions of any tree TT has the κ\kappa-EPP for every uncountable cardinal κ\kappa, and if TT is rayless, also the 0\aleph_0-EPP and the EPP.

Keywords

Cite

@article{arxiv.2411.02561,
  title  = {The Erd\H{o}s-P\'osa property for infinite graphs},
  author = {Thilo Krill},
  journal= {arXiv preprint arXiv:2411.02561},
  year   = {2024}
}

Comments

25 pages, 5 figures