Bohr sets in sumsets III: expanding difference sets and almost Bohr sets

Pierre-Yves Bienvenu, John T. Griesmer, Anh N. Le +1

Let $G$ be a discrete abelian group. Følner showed that if $A\subseteq G$ has positive upper Banach density, then $A-A$ contains an almost Bohr set -- a set of the form $B \setm…