Packing odd $T$-joins with at most two terminals

Abstract

Take a graph $G$, an edge subset $Σ\subseteq E(G)$, and a set of terminals $T\subseteq V(G)$ where $|T|$ is even. The triple $(G,Σ,T)$ is called a signed graft. A $T$-join is odd if it contains an odd number of edges from $Σ$. Let $ν$ be the maximum number of edge-disjoint odd $T$-joins. A signature is a set of the form $Σ\triangle δ(U)$ where $U\subseteq V(G)$ and $|U\cap T)$ is even. Let $τ$ be the minimum cardinality a $T$-cut or a signature can achieve. Then $ν\leq τ$ and we say that $(G,Σ,T)$ packs if equality holds here. We prove that $(G,Σ,T)$ packs if the signed graft is Eulerian and it excludes two special non-packing minors. Our result confirms the Cycling Conjecture for the class of clutters of odd $T$-joins with at most two terminals. Corollaries of this result include, the characterizations of weakly and evenly bipartite graphs, packing two-commodity paths, packing $T$-joins with at most four terminals, and a new result on covering edges with cuts.