Groups and Intervals in finite fields
In 1983, Erdos & Szemeredi proved a remarkable result, nowadays known as the sum-product theorem.
It asserts that a set of integers A cannot simultaneously have a small sum-set $\{a1 + a2 : a_1, a_2 \in A\}$
and a small product-set $\{a_1a_2 : a_1, a_2 \in A\}$. That is, it cannot behave as an arithmetic progression
as well as a geometric progression. Since that time there has been an explosion of work in this direction:
Bourgain–Katz–Tao, Solymosi, Garaev, Rudnev, Konyagin–Shkredov and many others. Similar results