Local avoidance conjecture for polynomial images of integers and primes

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Let h∈Z[x]h\in\mathbb{Z}[x] be a nonzero polynomial, and let X=h(Z)X=h(\mathbb{Z}) or X=h(P)X=h(\mathcal{P}), where P\mathcal{P} denotes the set of primes. For each m∈Nm\in\mathbb{N}, let XmX_m be the set of congruence classes modulo mm that intersect XX, and define

dX(m)=max⁡{∣A∣:A⊆Z/mZ, (A−A)∩Xm=∅}.d_X(m)=\max\{|A|: A\subseteq\mathbb{Z}/m\mathbb{Z},\ (A-A)\cap X_m=\emptyset\}.

Here μ(X)\mu(X) denotes the maximal density of an XX-set, namely a set whose pairwise differences avoid XX. Local avoidance conjecture. For every such hh and XX, we have

μ(X)=sup⁡m∈NdX(m)m.\mu(X)=\sup_{m\in\mathbb{N}}\frac{d_X(m)}{m}.

The conjecture asserts that for polynomial images of the integers and primes, the maximal global density of a set avoiding XX-differences is determined by the strongest finite-modulus local avoidance obstruction. It extends the principle that local obstructions are the only obstructions in intersectivity questions; the supplied context does not state whether it is known or open.

References

Primary source

Christian Dean, Haley Havard, Elizabeth Hawkins, Patch Heard, Andrew Lott and Alex Rice, “Notes and computations on forbidden differences”, arXiv:2508.03650 (2025).

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