\begin{definition}[Definition:Class Surjection]
Let $A$ and $B$ be classes.
Let $f: A \to B$ be a class mapping from $A$ to $B$.
Then $f$ is said to be a '''class surjection''' {{iff}}:
:$\forall y \in B: \exists x \in A: \map f x = y$
\end{definition}