Let $G$ be a finite abelian group of torsion $r$ and let $A$ be a subset of $G$.
The Freiman-Ruzsa theorem asserts that if $|A+A| \le K|A|$
then $A$ is contained in a coset of a subgroup of $G$ of size at most $K^2 r^{K^4} |A|$. It was ... more >>>