How does one prove that A intersecting B = A , iff A is a subset of B ?
Suppose A and B are subsets of U . How do you show that below , if any one of the relations stated holds , then each of the others holds : A ⊆ B , U ∖ A ⊇ U ∖ B , A ∪ B = B , A ∩ B = A ?