On a theorem of Shkredov

Abstract

We show that if A is a finite subset of an abelian group with additive energy at least c|A|^3 then there is a subset L of A with |L|=O(c^{-1}\log |A|) such that |A \cap Span(L)| >> c^{1/3}|A|.

5 pp. Included refinement from c^{1/2} to c^{1/3}, independently discovered by Shkredov and Yekhanin in arXiv:1004.2294. Corrected typos