Definition:Bijection/Definition 4

Definition
A mapping $f \subseteq S \times T$ is a bijection :
 * for each $y \in T$ there exists one and only one $x \in S$ such that $\tuple {x, y} \in f$.

Also see

 * Equivalence of Definitions of Bijection


 * Injection is Bijection iff Inverse is Injection