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Erdős problem 786

Let ϵ>0\epsilon > 0. Is there some set A⊂NA\subset\mathbb{N} of density >1−ϵ> 1 - \epsilon such that a1⋯ar=b1⋯bsa_1\cdots a_r = b_1\cdots b_s with ai,bj∈Aa_i, b_j\in A can only hold when r=sr = s?

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FormalConjectures/ErdosProblems/

786.lean

Retained formal statement4 of 7

An example of such a set with density 14\frac 1 4 is given by the integers ≡2(mod4)\equiv 2\pmod{4}

FormalConjectures/ErdosProblems/786.leanErdos786.erdos_786.parts.i.example1 lineExact file
∀ (A : Set ℕ), A = {n | n % 4 = 2} → A.HasDensity (1 / 4) ∧ Erdos786.Set.IsMulCardSet A
TextbookStatement only, no proof