Approximate Seymour second neighbourhood conjecture

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Let GG be an oriented graph, and let N1+(G,v)N^+_1(G,v) and N2+(G,v)N^+_2(G,v) denote the first and second out-neighbourhoods of vv.

Approximate Seymour conjecture. For every ϵ>0\epsilon>0, every oriented graph GG has at least one vertex vv satisfying

∣N2+(G,v)∣≥(1−ϵ)∣N1+(G,v)∣.|N^+_2(G,v)| \geq (1-\epsilon)|N^+_1(G,v)|.

The paper states this as an equivalent reformulation of Seymour's second neighbourhood conjecture, obtained using lexicographic products; it remains open together with the original conjecture.

References

Primary source

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

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