IMPORTANT RULES AND RESULTS OF THE SET
1) X ⋃ X = X , 4) X ⋂ φ = φ , 7) X ⋃ X’ = U
2) X ⋂ X = X , 5) X ⋃ U = U , 8) X ⋂ X’ = φ
3) X ⋃ φ = X , 6) X ⋂ U = X , 9) n(X’)= n(U) – n(X)
10) n( X ⋃ Y ) = n(X) + n(Y) – n (X ⋂ Y ) if X & Y are overlapping set
11) n( X ⋃ Y ) = n(X) + n(Y) , if X & Y are disjoint set