Binary Operations
The union of two sets A and B is denoted A ∪ B and
is defined as A ∪ B = x.
The intersection of two sets A and B is denoted A∩B
and is defined as A ∩ B = x ∈ A and x ∈ B.
Two sets are disjoint if they have no elements in common,
that is, A and B are disjoint if A ∩ B = ∅.