Question

1) Prove that if A and B are countable, then \[A \cap B\] is also countable.
2) Prove A\(A\B)=B\(B\A)

Answer 1

A n B can never be greater than A and B ........ So 0<=A n B <=A and 0<=A n B <=B...... THus, if A and B are countable ......... A n B is also countable