For 10 points, name this arithmetic operation, the inverse of subtraction.
In category theory, this concept is generalized by the coproduct, and its analogue in set theory is the disjoint union. Performing this operation on several vector spaces gives the smallest vector space containing each of the original vector spaces. For two vectors, it can be visualized using the parallelogram rule. Repeated application of this operation is denoted by a capital sigma. It is commutative and associative, and multiplication distributes over it. For 10 points, name this arithmetic operation, the inverse of subtraction.
In category theory, this concept is generalized by the coproduct, and its analogue in set theory is the disjoint union.
{addition} or {summation}