Two sets A_1 and A_2 are disjoint if their intersection A_1 intersection A_2 congruent ∅, where ∅ is the empty set. n sets A_1, A_2, ..., A_n are disjoint if A_i intersection A_j congruent ∅ for i!=j. For example, {A, B, C} and {D, E} are disjoint, but {A, B, C} and {C, D, E} are not. Disjoint sets are also said to be mutually exclusive or independent.