Thomassen's theorem on the two-linkage problem in acyclic digraphs: a shorter proof
Combinatorics
2024-09-17 v1
Abstract
Let G be an acyclic digraph, and let a, b, c, d be vertices, where a, b are sources, c, d are sinks, and every other vertex has in-degree and out-degree at least two. In 1985, Thomassen showed that there do not exist disjoint directed paths from a to c and from b to d, if and only if G can be drawn in a closed disc with a, b, c, d drawn in the boundary in order. We give a shorter proof.
Cite
@article{arxiv.2409.09758,
title = {Thomassen's theorem on the two-linkage problem in acyclic digraphs: a shorter proof},
author = {Paul Seymour},
journal= {arXiv preprint arXiv:2409.09758},
year = {2024}
}