Union of Sets

If A and B are sets, we define their union as the set consisting of all elements that belong to A or B and denoted it by A U B, is { x | x ∈ A or x ∈ B }

Intersection of Sets

The intersection of sets A and B, denoted by A ∩ B, is { x | x ∈ A ∧ x ∈ B }

Disjoint of Sets

Note if the intersection is empty, then A and B are said to be disjoint.