\begin{definition}[Definition:Class Injection]
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 injection''' {{iff}}:
:$\forall x_1, x_2 \in A: \map f {x_1} = \map f {x_2} \implies x_1 = x_2$
\end{definition}