A D18: Map $g : Y \to X$ is an inverse of $f$ if and only if
| (1) | \begin{equation} \forall \, x \in X : g(f(x)) = x \end{equation} | (D525: Left inverse map) |
| (2) | \begin{equation} \forall \, y \in Y : f(g(y)) = x \end{equation} | (D526: Right inverse map) |
| (1) | \begin{equation} \forall \, x \in X : g(f(x)) = x \end{equation} | (D525: Left inverse map) |
| (2) | \begin{equation} \forall \, y \in Y : f(g(y)) = x \end{equation} | (D526: Right inverse map) |