Two sets are called disjoint if they have no elements in common, i.e., if their intersection is the empty set. Prove that finite sets A and B are disjoint if and only if |A|+|B|=|A \cup B|.∣A∣+∣B∣=∣A∪B∣. Use the definition of \emptyset∅ and the inclusion-exclusion principle in your proof.
