• set is a collection of elements in which there are no duplicates.
  • The union of sets A and B (A ∪ B or A + B) is the set of all elements that are contained in either A or B (or both). Note that the result is still a set (no duplicates) even if an element is in both A and B. Union is commutative, meaning A ∪ B == B ∪ A.