A small-doubling structural conjecture for finite sets of integers

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Let AA be a finite set of integers, and write A−A={a−a′:a,a′∈A}A-A=\{a-a':a,a'\in A\}. Small-doubling structural conjecture. There exists a natural number KK such that, whenever ∣A∣≥K|A|\ge K and

∣A−A∣=3∣A∣−3+r|A-A|=3|A|-3+r

for an integer rr satisfying 0<r<13∣A∣−20<r<\tfrac13|A|-2, one of the following holds: (i) AA is contained in an arithmetic progression of length 2∣A∣−1+2r2|A|-1+2r; or (ii) A⊆P1∪P2A\subseteq P_1\cup P_2 for arithmetic progressions P1,P2P_1,P_2 with common step and ∣P1∣+∣P2∣≤∣A∣+r|P_1|+|P_2|\le |A|+r. The source proposes this conjecture as a replacement for Jin's inverse theorem in order to obtain a reasonable value of a structural threshold. Its resolution is not stated, so it remains open.

References

Primary source

Tuan Tran, “On the structure of large sum-free sets of integers”, arXiv:1705.02584 (2018).

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