Inverse of Inverse of Bijection/Proof 2

Theorem
Let $f: S \to T$ be a bijection.

Then:
 * $\left({f^{-1}}\right)^{-1} = f$

where $f^{-1}$ is the inverse of $f$.

Proof
A mapping is a relation.

Thus it follows that Inverse of Inverse Relation can be applied directly.