MSTD sets and Freiman isomorphisms
  An MSTD set is a finite set with more pairwise sums than differences. $(\Upsilon,\Phi)$-ismorphisms are generalizations of Freiman isomorphisms to arbitrary linear forms. These generalized isomorphisms are used to prove that every finite set of real numbers is Freiman isomorphic to a finite set of integers. This implies that there exists no MSTD set $A$ of real numbers with $|A| \leq 7$, and, up to Freiman isomorphism, there exists exactly one MSTD set $A$ of real numbers with $|A| = 8$. 
Melvyn B. Nathanson
math.NT