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Statement

Erdos and Graham asked whether a positive-density subset of {1,…,N}\{1,\ldots,N\} can avoid having any two distinct elements a,ba,b whose unit fractions average to a unit fraction. It can: there is a constant c>0c>0 such that for all large NN some A⊆{1,…,N}A \subseteq \{1,\ldots,N\} of size >cN> cN has that property, which also gives the best known lower bounds for related unit-fraction avoidance problems.

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  1. construction · #1

    Will Sawin, using ChatGPT

    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 assisted
    — a person led the work and used a model along the way.

    The author gives a narrative rather than a blanket acknowledgement. Starting from a computation of Stijn Cambie, he asked ChatGPT to look for patterns in Cambie's extremal set that might suggest a generalization; it observed that in a pair with a given ratio the larger element is usually absent unless the smaller is absent for other reasons, and described a change of variables. Dropping the hedges in that observation gives the set the paper analyzes, which turns out to be essentially where Hooley's function takes its minimum value. The model was also used for reference search and proofreading.

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