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Pace Nielsen
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Unique product groups (and semigroups)

A group $G$ is called a u.p.-group (short for unique product group) if for all nonempty finite subsets $A,B\subseteq G$, there exists an element $g\in A \cdot B$ which can be uniquely written as a product $g=ab$ for some $a\in A$ and $b\in B$.

My question is: Does there exist a u.p.-group (or even u.p.-semigroup) for which the corresponding property with three sets $A,B,C$ doesn't hold? Necessarily, such a group would not be orderable, so such an example might be difficult to find.

Pace Nielsen
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