Let $f : X \to Y$ be a D18: Map such that
| (i) | $f^{-1} : Y \to X$ is an D216: Inverse map for $f$ |
Then $f$ is an D216: Inverse map for $f^{-1}$.
| (i) | $f^{-1} : Y \to X$ is an D216: Inverse map for $f$ |