Hildebrand's nonemptiness conjecture for consecutive stable-set intersections

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Let S⊆N\mathcal{S}\subseteq\mathbb{N} be a stable set, meaning that for every natural number dd, the set of nn for which membership of nn and dndn in S\mathcal{S} differs has density 00.

Hildebrand's nonemptiness conjecture. If S\mathcal{S} has positive lower density, then for every natural number kk,

S∩(S+1)∩(S+2)∩⋯∩(S+(k−1))≠∅.\mathcal{S}\cap(\mathcal{S}+1)\cap(\mathcal{S}+2)\cap\cdots\cap(\mathcal{S}+(k-1))\neq\varnothing.

The source presents this as a weaker version of Hildebrand's density conjecture and notes that it is equivalent to positivity of the upper density of the same intersection. Since the paper's counterexample targets the stronger positive-lower-density assertion, the status of this weaker formulation should be checked separately.

References

Primary source

Redmond McNamara, “A counterexample to Hildebrand's conjecture on stable sets”, arXiv:2312.08544 (2025).

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