Definition:Surjection/Class Theory

Definition
Let $A$ and $B$ be classes.

Let $f: A \to B$ be a mapping from $A$ to $B$.

Then $f$ is a surjection :
 * $\Img f = B$

where $\Img f$ denotes the image of $f$.

That is, :
 * $\forall y \in B: \exists x \in A: \map f x = y$

Also see

 * Definition:Injection (Class Theory)