Generalized unbounded improvement conjecture for (k,)(k,\ell)-sum-free sets

Let k<k<\ell be positive integers. For a set AA of NN positive integers, let M(k,)(A)\mathscr{M}_{(k,\ell)}(A) be the size of its largest (k,)(k,\ell)-sum-free subset, where a set is (k,)(k,\ell)-sum-free if, for every k+k+\ell elements x1,,xk,y1,,yx_1,\dots,x_k,y_1,\dots,y_\ell, one has

i=1kxij=1yj.\sum_{i=1}^{k}x_i\ne\sum_{j=1}^{\ell}y_j.

Define

M(k,)(N)=infAZ>0, A=NM(k,)(A).\mathscr{M}_{(k,\ell)}(N)=\inf_{A\subseteq\mathbb{Z}^{>0},\ |A|=N}\mathscr{M}_{(k,\ell)}(A).

A generalized (k,)(k,\ell)-sum-free conjecture. There is a function ω(N)\omega(N)\to\infty as NN\to\infty such that for every set AA of NN positive integers, there exists a maximal (k,)(k,\ell)-sum-free set Ω(k,)R/Z\Omega(k,\ell)\subseteq\mathbb{R}/\mathbb{Z} for which

maxxR/ZnA(\mathbbm1Ω(k,)1k+)(nx)=ω(N).\max_{x\in\mathbb{R}/\mathbb{Z}}\sum_{n\in A}\left(\mathbbm{1}_{\Omega(k,\ell)}-\frac{1}{k+\ell}\right)(nx)=\omega(N).

The known asymptotic formula M(k,)(N)=N/(k+)+o(N)\mathscr{M}_{(k,\ell)}(N)=N/(k+\ell)+o(N) leaves open whether every pair (k,)(k,\ell) admits an unbounded improvement over the probabilistic baseline N/(k+)N/(k+\ell).

Sources & referencesView supporting material

Primary source

Yifan Jing and Shukun Wu, “A note on the largest sum-free sets of integers”, arXiv:2011.09963 (2023).

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