Let $A$ be a finite, nonempty subset of an abelian group, and let $2A:=\{a+b\colon a,b\in A\}$ and $A-A:=\{a-b\colon a,b\in A\}$ denote the sumset and the difference set of $A$, respectively.

If every non-zero element of $A-A$ has a unique representation as $a-b$ with $a,b\in A$, then all sums $a+b$ are pairwise distinct; as a result, $A$ is a Sidon set and $|2A|=\frac12|A|(|A|+1)$. Suppose now that only, say, $k$ elements of $A-A$ are known to be uniquely representable; how large must $|2A|$ be in this case? I am specifically interested in the situation where $k=|A|+1$.

Another way to cast the problem is as follows. If there is a group element with a unique representation in $A-A$, then $|2A|\ge 2|A|-1$. How large must $|2A|$ be given that $A-A$ has at least $|A|+1$ uniquely representable elements?

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