In this context, A is a set, and A + A represents the set of all sums of pairs of elements drawn from A.
The paper doesn't use A^2, but rather |A|^2, which is ordinary squaring of an integer. It does use AA, which is the set of products of pairs of elements drawn from A.
Comments
That is just exponentiation, eg squaring. They’re just putting symbols instead of numbers there.
But then they say A + A <= A^2, wouldn’t that be false for a = 1?
In this context, A is a set, and A + A represents the set of all sums of pairs of elements drawn from A.
The paper doesn't use A^2, but rather |A|^2, which is ordinary squaring of an integer. It does use AA, which is the set of products of pairs of elements drawn from A.