A counterexample to Hickingbotham's conjecture about $k$-ghost-edges
Combinatorics
2026-02-04 v1
Abstract
Fix and let be a connected graph with . We say that is a {\em -ghost-edge} of if for every tree decomposition of with width at most , the set is contained in a bag of . Although a -ghost-edge of is not an edge of , but it behaves like real edges with respect to tree decomposition of with width at most . For any graph with treewidth and , when there are at least internally vertex disjoint -paths, Hickingbotham proved that is a -ghost-edge of ; while when there are at most internally vertex disjoint -paths, he conjectured that it is not a -ghost-edge of . In this paper, we prove that this conjecture is wrong.
Cite
@article{arxiv.2602.03016,
title = {A counterexample to Hickingbotham's conjecture about $k$-ghost-edges},
author = {Rong Chen},
journal= {arXiv preprint arXiv:2602.03016},
year = {2026}
}