Fan's weighted refinement of the 4-flow conjecture

Let GG be a graph with a circuit CC, and let ω:E(G)Z\omega:E(G)\to\mathbb{Z} be an integer edge-weight function. A Z2×Z2\mathbb{Z}_2\times\mathbb{Z}_2-flow is a flow with values in the abelian group Z2×Z2\mathbb{Z}_2\times\mathbb{Z}_2; for such a flow hh, write Eh=(0,0)(C)E_{h=(0,0)}(C) for the edges of CC on which hh has value (0,0)(0,0), and write ω(S)=eSω(e)\omega(S)=\sum_{e\in S}\omega(e).

Fan's weighted refinement. If there is a Z2×Z2\mathbb{Z}_2\times\mathbb{Z}_2-flow ff such that

E(G)E(C)supp(f),E(G)-E(C)\subseteq \operatorname{supp}(f),

then there is a Z2×Z2\mathbb{Z}_2\times\mathbb{Z}_2-flow gg in GG such that

E(G)E(C)supp(g)E(G)-E(C)\subseteq \operatorname{supp}(g)

and

ω(Eg=(0,0)(C))<14ω(C).\omega\bigl(E_{g=(0,0)}(C)\bigr)<\frac{1}{4}\omega(C).

This is presented as a refinement of Fan's conjecture and would control the weighted contribution of zero-valued edges on the circuit. Its resolution is not given in the supplied text.

Sources & referencesView supporting material

Primary source

Deping Song, Shuang Li and Xiao Wang, “On Fan's conjecture about 4-flow”, arXiv:2306.01493 (2023).

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