Kawarabayashi–Picasarri-Arrieta dichromatic bound conjecture

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Let DD be a digraph. Define

Δ~(D)=max⁡v∈V(D)d−(v)d+(v),\widetilde{\Delta}(D)=\max_{v\in V(D)}\sqrt{d^-(v)d^+(v)},

and let ↔tinyω(D)\overset{\text{tiny}}{\leftrightarrow}{\omega}(D) be the largest size of a biclique in DD. Let χ⃗(D)\vec{\chi}(D) denote the dichromatic number of DD. Kawarabayashi–Picasarri-Arrieta conjecture. Every digraph DD satisfies

χ⃗(D)≤⌈12(Δ~(D)+1+↔tinyω(D))⌉.\vec{\chi}(D) \leq \left\lceil \frac{1}{2}\left(\widetilde{\Delta}(D)+1+\overset{\text{tiny}}{\leftrightarrow}{\omega}(D)\right)\right\rceil.

If true, this would imply Reed's conjecture and an independent conjecture of Harutyunyan and Mohar. The conjecture is presented as open in the source.

References

Primary source

Ken-ichi Kawarabayashi and Lucas Picasarri-Arrieta, “Coloring digraphs with Δ-b colors”, arXiv:2607.06928 (2026).

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