Some conjectures on $r$-graphs and equivalences
An $r$-regular graph is an $r$-graph, if every odd set of vertices is connected to its complement by at least $r$ 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 $r...
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Zusammenfassung: | An $r$-regular graph is an $r$-graph, if every odd set of vertices is
connected to its complement by at least $r$ 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
$r$-graph is $r$-edge colorable and (2) that every $r$-graph has $2r$ perfect
matchings such that every edge is contained in precisely two of them. We study
several variants of these conjectures.
A $(t,r)$-PM is a multiset of $t \cdot r$ perfect matchings of an $r$-graph
$G$ such that every edge is in precisely $t$ of them. We show that the
following statements are equivalent for every $t, r \geq 1$:
1. Every planar $r$-graph has a $(t,r)$-PM.
2. Every $K_5$-minor-free $r$-graph has a $(t,r)$-PM.
3. Every $K_{3,3}$-minor-free $r$-graph has a $(t,r)$-PM.
4. Every $r$-graph whose underlying simple graph has crossing number at most
$1$ has a $(t,r)$-PM. |
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DOI: | 10.48550/arxiv.2411.01753 |