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

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Let k<ℓk<\ell be positive integers. For a set AA of NN positive integers, let M(k,ℓ)(A)\mathscr{M}_{(k,\ell)}(A) be the size of its largest (k,ℓ)(k,\ell)-sum-free subset, where a set is (k,ℓ)(k,\ell)-sum-free if, for every k+ℓk+\ell elements x1,…,xk,y1,…,yℓx_1,\dots,x_k,y_1,\dots,y_\ell, one has

∑i=1kxi≠∑j=1ℓyj.\sum_{i=1}^{k}x_i\ne\sum_{j=1}^{\ell}y_j.

Define

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

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

max⁡x∈R/Z∑n∈A(1Ω(k,ℓ)−1k+ℓ)(nx)=ω(N).\max_{x\in\mathbb{R}/\mathbb{Z}}\sum_{n\in A}\left(\mathbb{1}_{\Omega(k,\ell)}-\frac{1}{k+\ell}\right)(nx)=\omega(N).

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

References

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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