1. The problem statement, all variables and given/known data Let f be a function on A onto B where B is a subset of A, and f is a one-to-one function. Now, I want to show that B can't be a proper subset of A( that is, not B[itex]\subset[/itex]A. this means B=A). 2. Relevant equations 3. The attempt at a solution I attempted to solve this problem. Even though it is not complicated problem, but I don't have an idea how to prove it. Could you give me a clue or something??