a set is a collection of objects (called members or elements) that is regarded as being a single object. To indicate that an object x is a member of a set A one writes x ∊ A, while x ∉ A indicates that x is not a member of A.

*A*∪*B*—read “*A*union*B*” or “the union of*A*and*B*”*A*∩*B*—read “*A*intersection*B*” or “the intersection of*A*and*B*”*U*is called the universal set*A*′ or*U*−*A*is called as complement of A- Cartesian product: Let A and B be two sets. Cartesian product of A and B is denoted by A × B, is the set of all ordered pairs (a,b), where a belong to A and B belong to B.

A × B = {(a, b) | a ∈ A ∧ b ∈ B}

- if every element in A is also in B and every element in B is in A; symbolically, x ∊ A implies x ∊ B and vice versa.