The fractional chromatic conjecture for 4-cycle-free planar graphs

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Let GG be a 4-cycle-free planar graph, and let χf(G)\chi_f(G) denote its fractional chromatic number. Fractional chromatic conjecture. There exists some ϵ>0\epsilon>0 such that

χf(G)≤4−ϵ.\chi_f(G)\leq 4-\epsilon.

The conjecture asks for a uniform improvement over the Four Color Theorem for the fractional chromatic number of 4-cycle-free planar graphs. The supplied text presents it as an open question, and no resolution is given in the status evidence.

References

Primary source

Tom Kelly, Sid Kolichala, Caleb McFarland and Jatong Su, “The independence ratio of 4-cycle-free planar graphs”, arXiv:2305.02414 (2026).

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