For any two sets A and B, show that the following statements are equivalent:
A ∩ B = A.
Finally, now we need to show 4 ⇒ 1.
So, assume A ∩ B = A.
To show: A ⊂ B
∵A ∩ B = A, therefore A⊂B, and so (4) ⇒ (1) is true.