Injective, Surjective and Bijective Functions between Classes

In the setting of Class Theory NBG: the Axioms, Standing Conventions and Basic Notation, let $A$ and $B$ be classes and let $F:A\to B$ be a map; for $u\in A$, $F(u)$ is the value of $F$ at $u$.

¶ $F$ is injective (one-to-one) if, for all sets $u,u'\in A$, $F(u)=F(u')$ implies $u=u'$.

¶ $F$ is surjective (maps $A$ onto $B$) if, for every set $v\in B$, there is a set $u\in A$ with $F(u)=v$.

¶ $F$ is bijective, or a bijection from $A$ to $B$, if it is both injective and surjective.