Frankl–Győri–He–Lv–Salia–Tompkins–Varga–Zhu conjecture for Gallai 3-colouring templates

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Let h:[0,1]→Rh:[0,1]\to\mathbb{R} be defined by

h(x)=(x2+(1−x)2)x2(1−x2),h(x)=\left(x^2+(1-x)^2\right)x^2\left(1-x^2\right),

and let υ∈[0,1]\upsilon\in[0,1] maximise hh. Let G=(G1,G2,G3)\mathbf{G}=(G_1,G_2,G_3) be a Gallai 33-colouring template on nn vertices, meaning that its three colour classes partition the pairs of vertices and contain no rainbow triangle.

Frankl–Győri–He–Lv–Salia–Tompkins–Varga–Zhu conjecture. As nn tends to infinity,

(∣E(G1)∣⋅∣E(G2)∣⋅∣E(G3)∣)13≤(h(υ)+o(1))13(n2).\Bigl(\lvert E(G_1)\rvert\cdot\lvert E(G_2)\rvert\cdot\lvert E(G_3)\rvert\Bigr)^{\frac13}\leq\left(h(\upsilon)+o(1)\right)^{\frac13}\binom{n}{2}.

The conjecture asserts that the construction H(⌈υn⌉,n−⌈υn⌉,0)\mathbf{H}(\lceil\upsilon n\rceil,n-\lceil\upsilon n\rceil,0) is asymptotically optimal. It was proposed after that construction disproved Frankl's earlier upper bound; the supplied text gives no resolution of this conjecture.

References

Primary source

Victor Falgas-Ravry, Klas Markström and Eero Räty, “Rainbow variations on a theme by Mantel: extremal problems for Gallai colouring templates”, arXiv:2212.07180 (2024).

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