Past exam of the mathematics course of the University of Cambridge / 2019 / iii / Paper 149 / 1 / a

The Plünnecke-Ruzsa inequality states that, for all nonnegative integers $m,n$,Here $mA$ is the iterated sumset of $m$ copies of $A$, with $0A=\{0\}$. In particular, $|mA|\le K^m|A|$.