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Statement

Let A={1≤a1<a2<⋯ }A=\{1\leq a_1< a_2<\cdots\} be a set of integers such that A\BA\backslash B is complete for any finite subset BB and not complete for any infinite subset BB. If an+1/an≥1+ϵa_{n+1}/a_n \geq 1+\epsilon for all nn, must lim⁡nan+1/an=(1+5)/2\lim_n a_{n+1}/a_n=(1+\sqrt{5})/2? Under the reading where the ratio limit is assumed to exist, a Lean-verified argument forces the limit to be the golden ratio; a separate construction disproves the literal statement where convergence is not assumed.

Record

Comments

No person has examined this. Everything below was judged by machines. say whether it holds →

  1. proof attempt · #1

    Kenta Kitamura, using ChatGPT, Codex

    That credit came with the record as it was imported. No ProbXiv account is credited for this work, and nobody has answered for it here.

    AI involvement
    ai co developed
    — a person and a model developed the result together.

    Kitamura's affirmative Lean 4 formalization of the limit-exists reading was produced with ChatGPT and Codex; days earlier, GPT Pro with Codex had produced a Lean-checked disproof of the literal reading (Liam Price), which the forum classes as solving a variant with precursors in Burr-Erdős 1981.

  2. Machine-checked by Lean on #1 · not a person

    lean: correctLean

    scope Lean formalization of the result

    A community screening found the Lean of the variant disproof correct and corresponding to its paper (one typo); the affirmative limit-exists formalization reports standard axioms only. erdosproblems.com still lists the problem open.

    Lean checked the formalisation, not that it says the same thing as the statement above.

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Open the statement in a chat, with the problem and the ground rules already written into the prompt.

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