Suppose U is a set and A⊆ U. the complement of A in U is the set of all those elements of U which are not members of A. This is denoted by
AC or A’. Thus,
A’ = { x : x ∈ U but x∉ A}
For any subset A of U, we have A∩A’ = ∅ and AUA’ = U.
For any set U, U’ = ∅ and ∅’ = U.
