The sumset of the subsets $A$ and $B$ of an additively written group is defined by $A+B:=\{a+b\colon a\in A,\ b\in B\}$. The basic idea to add sets has been around since Cauchy at least.
Erdős and Heilbronn considered a variation where equal summands are excluded from consideration. This version of set addition was further generalized to consider restricted sumsets where the sums allowed are taken "along the edges of a graph": that is, given a set $E\subseteq A\times B$, we let $A\stackrel{E}{+}B:=\{a+b\colon a\in A,\ b\in B,\ (a,b)\in E\}$. Perhaps, the most famous result where restricted sumsets play a central role is the Balog-Szemerédi-Gowers theorem.
I am interested in the historical component of the story.
- When and where restricted sumsets of a general form (that is, the addition of sets along a graph) were introduced?
- Who has coined the name "restricted sumset"?
- Where does the notation $A\stackrel{E}{+}B$ originate from?