The gap-cycle conjecture for 2-coloring simple planar digraphs

Let DD be a simple planar digraph. Say that DD has no cycles of lengths 4,,k4,\dots,k when it contains no directed cycles whose lengths are among those integers. Gap-cycle conjecture. There exists kk such that every simple planar digraph without cycles of length 4,,k4,\dots,k is 2-colorable. This is presented as a relaxation of the Neumann-Lara–Škrekovski conjecture; the source says that even the original conjecture remains out of reach, so this question is open.

Sources & referencesView supporting material

Primary source

Ararat Harutyunyan and Bojan Mohar, “Planar digraphs of digirth five are 2-colorable”, arXiv:1401.2213 (2014).

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