English

Some conjectures on $r$-graphs and equivalences

Combinatorics 2026-05-29 v2

Abstract

An rr-regular graph is an rr-graph, if every odd set of vertices is connected to its complement by at least rr edges. Seymour [On multicolourings of cubic graphs, and conjectures of Fulkerson and Tutte.~\emph{Proc.~London Math.~Soc.}~(3), 38(3): 423-460, 1979] conjectured (1) that every planar rr-graph is rr-edge colorable and (2) that every rr-graph has 2r2r perfect matchings such that every edge is contained in precisely two of them. We study several variants of these conjectures. A (t,r)(t,r)-PM is a multiset of trt \cdot r perfect matchings of an rr-graph GG such that every edge is in precisely tt of them. We show that the following statements are equivalent for every t,r1t, r \geq 1: 1. Every planar rr-graph has a (t,r)(t,r)-PM. 2. Every K5K_5-minor-free rr-graph has a (t,r)(t,r)-PM. 3. Every K3,3K_{3,3}-minor-free rr-graph has a (t,r)(t,r)-PM. 4. Every rr-graph whose underlying simple graph has crossing number at most 11 has a (t,r)(t,r)-PM.

Keywords

Cite

@article{arxiv.2411.01753,
  title  = {Some conjectures on $r$-graphs and equivalences},
  author = {Yulai Ma and Eckhard Steffen and Isaak H. Wolf and Junxue Zhang},
  journal= {arXiv preprint arXiv:2411.01753},
  year   = {2026}
}

Comments

11 pages, 1 figure. Minor typos corrected

R2 v1 2026-06-28T19:46:47.566Z