Do there exist sets $X \subset A \subset \mathbb{Z}$ such that $$\frac{|A+X|}{|X|} < \frac{|A+A|}{|A|} $$?
I would also be happy if one can replace $\mathbb{Z}$ with any other abelian group.
Do there exist sets $X \subset A \subset \mathbb{Z}$ such that $$\frac{|A+X|}{|X|} < \frac{|A+A|}{|A|} $$?
I would also be happy if one can replace $\mathbb{Z}$ with any other abelian group.
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