Cyclic interval conjecture for odd cycles

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Let mm be odd and let x⊆Zmx\subseteq\mathbb{Z}_m with x∉{∅,Zm}x\notin\{\emptyset,\mathbb{Z}_m\}. An arc WW is a cyclic interval in Zm\mathbb{Z}_m. Write CmC_m for the cycle graph on mm vertices, and let kmin⁡(Cm)k_{\min}(C_m) denote the minimum dimension of an isometric embedding of CmC_m into an abelian group. The lemma asserts that there is an arc WW satisfying

∣W△x∣<min⁡(∣W∣,m−∣W∣).|W\triangle x|<\min(|W|,m-|W|).

Cyclic interval conjecture. The displayed inequality holds for every odd mm and every nonempty proper subset x⊆Zmx\subseteq\mathbb{Z}_m; consequently,

kmin⁡(Cm)=m−1k_{\min}(C_m)=m-1

for every odd cycle CmC_m.

The inequality is the remaining case beyond the covering-arc regime and has been verified exhaustively for all odd m≤17m\leq 17. If true, it gives the naive-dimension lower bound for every odd cycle; the general case remains open.

References

Primary source

Fokam Souop Rigobert and Bitjoka Laurent, “Minimal Isometric Embeddings of Graphs into Abelian Groups: Theory, Algorithms, and Applications to Signal Processing over Networks”, arXiv:2606.29391 (2026).

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