A note on Freiman models in Heisenberg groups

Norbert Hegyvári, François Hennecart

Green and Ruzsa recently proved that for any $s\ge 2$, any small squaring set $A$ in a (multiplicative) abelian group, i.e. $|A\cdot A|<K|A|$, has a Freiman $s$-model: it means that…