I hope I have not hereby created a duplicate, please perdon me if I did, but I had this question for a while now:
Let $A \& B $ be two sets such that $A \subseteq B$. Suppose there exist a one to one (bijective) function $f : A \to B $. Then have we got $|A| = |B|$?
I know that if these sets are finite, it works, but what about the infinite case