A, B are some finite subsets of a abelian group.
|A + B| ~ |A|
The problem is I couldn't precisely understand what does ~ mean in that case.
For example, it could be found in notes of Tao's lectures on Additive Combinatorics
Page 8, he is defining essentialy B-invariant set.
It is obvious that ~ means that A+B is not much larger than A but I need the precise definition. For me it's a bit too bad using ~ for something else than equivalence relation.
Thanks!