Kneser's theorem (combinatorics)

In the branch of mathematics known as additive combinatorics, Kneser's theorem can refer to one of several related theorems regarding the sizes of certain sumsets in abelian groups. These are named after Martin Kneser, who published them in 1953 and 1956.

Source: Wikipedia — Kneser's theorem (combinatorics) (CC BY-SA 4.0)