Sets

How can we say that B is a proper subset of A ? A union B would also be equal to B if B = A ? So shouldn’t we say that B is a subset of A instead of proper subset ?

in the above question B is a smallpart of A since( AB) union B = A so it is a proper subset

@HarshithaVanam But if B = A, (A  B) = ɸ.
So, (A  B) ∪ B = ɸ ∪ B = B = A
⇒ (A  B) ∪ B = A