Let $f : X \to Y$ be a D18: Map.
Then
| (1) | $f(f^{-1} B) \subseteq B$ for all $B \subseteq Y$ |
| (2) | $f(f^{-1} B) = B$ for all $B \subseteq Y$ if and only if $f$ is a D466: Surjective map |