Conjecture on valid orientations with four exceptional boundary vertices

Let GG be a plane graph with a valid prescription function p:V(G){1,0,1}p:V(G)\rightarrow\{-1,0,1\}, a specified face FGF_G, and at most four specified vertices d,r,s,td,r,s,t. The vertex dd, when present, is a degree-33 boundary vertex that may be oriented; each of r,s,tr,s,t, when present, is a degree-33 boundary vertex. Assume

G is 3-edge-connected,G\text{ is 3-edge-connected,}

GG has at most four 33-edge-cuts, only δ({d})\delta(\{d\}), δ({r})\delta(\{r\}), δ({s})\delta(\{s\}), or δ({t})\delta(\{t\}), and every vertex outside the boundary of FGF_G has five edge-disjoint paths to that boundary.

Conjecture on valid orientations with four exceptional boundary vertices. Then GG has a valid orientation.

This conjecture extends the paper's orientation theorem by allowing further degree-33 boundary vertices and is presented as best possible in view of related counterexamples.

Sources & referencesView supporting material

Primary source

Jamie V. de Jong, “Two Strong 3-Flow Theorems for Planar Graphs”, arXiv:2011.02140 (2020).

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