Intermediate fractional colorability conjecture for subcubic triangle-free graphs

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Let GG be a subcubic triangle-free graph, and let F14(1)F_{14}^{(1)}, F14(2)F_{14}^{(2)}, F11F_{11}, and F22F_{22} be the four specified graphs from the paper. Suppose that none of these graphs occurs as a subgraph of GG. A graph is fractionally rr-colorable when its fractional chromatic number is at most rr.

Intermediate fractional colorability conjecture. Every such graph GG is fractionally 19/719/7-colorable.

This conjecture is intermediate between the paper's 11/411/4 theorem under exclusion of F14(1)F_{14}^{(1)} and F14(2)F_{14}^{(2)} and the stronger 8/38/3 conjecture that additionally excludes F11F_{11}, F22F_{22}, F19(1)F_{19}^{(1)}, and F19(2)F_{19}^{(2)}. The supplied material gives no resolution status.

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Primary source

Zdeněk Dvořák, Bernard Lidický and Luke Postle, “11/4-colorability of subcubic triangle-free graphs”, arXiv:2204.12683 (2025).

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