English

Panchromatic patterns by paths

Combinatorics 2019-03-26 v1

Abstract

Let H=(VH,AH)H=(V_H,A_H) be a digraph, possibly with loops, and let D=(VD,AD)D=(V_D, A_D) be a loopless multidigraph with a colouring of its arcs c:ADVHc: A_D \rightarrow V_H. An HH-path of DD is a path (v0,,vn)(v_0, \dots, v_n) of DD such that (c(vi1,vi),c(vi,vi+1))(c(v_{i-1}, v_i), c(v_i,v_{i+1})) is an arc of HH for every 1in11 \le i \le n-1. For u,vVDu, v \in V_D, we say that uu reaches vv by HH-paths if there exists an HH-path from uu to vv in DD. A subset SVDS \subseteq V_D is HH-absorbent of DD if every vertex in VDSV_D-S reaches by HH-paths some vertex in SS, and it is HH-independent if no vertex in SS can reach another (different) vertex in SS by HH-pahts. An HH-kernel is an independent by HH-paths and absorbent by HH-paths subset of VDV_D. We define B~1\tilde{\mathscr{B}}_1 as the set of digraphs HH such that any HH-arc-coloured tournament has an HH-absorbent by paths vertex; the set B~2\tilde{\mathscr{B}}_2 consists of the digraphs HH such that any HH-arc-coloured digraph DD has an independent, HH-absorbent by paths set; analogously, the set B~3\tilde{\mathscr{B}}_3 is the set of digraphs HH such that every HH-arc-coloured digraph DD contains an HH-kernel by paths. In this work, we present a characterization of B~2\tilde{\mathscr{B}}_2, and provide structural properties of the digraphs in B~3\tilde{\mathscr{B}}_3 which settle up its characterization except for the analysis of a single digraph on three vertices.

Cite

@article{arxiv.1903.10031,
  title  = {Panchromatic patterns by paths},
  author = {Germán Benítez-Bobadilla and Hortensia Galeana-Sánchez and César Hernández-Cruz},
  journal= {arXiv preprint arXiv:1903.10031},
  year   = {2019}
}

Comments

27 pages, 9 figures