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Let . Is there some set of density such that with can only hold when ?
Similarly, can one always find a set with this property of size ?
Let . Is there some set of density such that with (where each product runs over a subset of ) can only hold when ?
Similarly, can one always find a set with this property of size ?
Source: erdosproblems.com/786
A full solution has been claimed but not yet accepted. The statement is false.
The site labels the problem OPEN (page last edited 11 April 2026;
proof-claim tab accessed 2026-10-06), a label that describes the
distinct-factor reading as unsettled. The standing derives from the claim
pages and judges the Statement (precise). The full claim
Li 2026, submitted
to the site's proof-claim tab on 28 September 2026 and declared as produced
with GPT-6 Astra and GPT-5.6 Sol (OpenAI) and Claude (Anthropic), asserts
negative answers to both questions under the distinct-factor reading; the
partial claim
Gessel 2026
of 6 September 2026 asserts the density bound for the first question
under the same reading. The site has not acted on either, neither has a
referee or named reviewer, and no Lean development of either has been built
or audited in this corpus, so the full claim is claimed and the problem's
standing is claimed, disproved. Ruzsa's negative answers to both questions
under the distinct-factor reading, which [Er80] reports without a proof or a
proof citation and which the site's commentary suspects came from a confusion
of the two conventions, are a report of an unpublished result rather than a
posted claim, so they have no claim page; Progress below records the report.
The negative answers under the repetitions-allowed reading concern the
reading not adopted and are recorded under Formulation.
The site's wording does not say whether a factor may repeat within a product, and the two readings have different answers on the record: when repetitions are allowed the condition on is stronger, and [ERS73] answers both questions no (see Formulation); when the factors of each product are distinct the condition is weaker, and the site's commentary calls both questions open. The site's commentary itself calls the original sources ambiguous on this point. The change inserts "(where each product runs over a subset of )" after "", in the words of Erdős's definition of property in [Er80], printed p. 114: "(where each product runs over a subset of the 's)". That is the poser's own statement of both questions, and it fixes the distinct-factor reading; the two subsets may overlap, since no disjointness is required there. The poser's other texts are silent but agree with it: [Er65], printed p. 182, introduces the condition (4), only if , as the alternative to the distinct-products condition (3), whose products are over subsets ( or ), [Er69], printed p. 81, display (12), writes only if , and [Er73], printed p. 132, writes the products as , neither saying whether the indices repeat. The silence is therefore already in the poser's earlier texts, and no text of his fixes the repetitions-allowed reading. The results about that reading are credited, not counted: Theorems 2 and 6 of Erdős, Ruzsa and Sárközy [ERS73], with the transfer to product sets that the site's commentary gives, and Tao's sharp constant from Granville and Soundararajan [GrSo01] in forum post 4061 (2 February 2026), all recorded under Formulation and Known Results.