Converse-invariance conjecture for regular Seymour-tight orientations

From papers

Let OO be an orientation, and write Ni(O,v)N^-_i(O,v) and Ni+(O,v)N^+_i(O,v) for the in- and out-neighbourhoods of distance ii from vv. Call OO Seymour-tight when N2+(O,v)=N1+(O,v)|N^+_2(O,v)|=|N^+_1(O,v)| for every vertex vv.

Converse-invariance conjecture. If

N1(O,v)=N1+(O,v)=N2+(O,v)=k|N^-_1(O,v)|=|N^+_1(O,v)|=|N^+_2(O,v)|=k

for all veV(O)v e V(O), then

N2(O,v)=k|N^-_2(O,v)|=k

for all vV(O)v\in V(O).

This would imply that the converse of every such regular Seymour-tight orientation is again Seymour-tight. Converse-invariance is known for vertex-transitive Seymour-tight orientations, but fails for general strongly connected Seymour-tight orientations; the stated weaker regularity condition remains open.

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Sources & referencesView supporting material

Primary source

Krystal Guo, Ross J. Kang and Gabriëlle Zwaneveld, “Seymour-tight orientations”, arXiv:2603.29626 (2026).

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