MathItems

Let $A$ and $B$ be two sets and let $f$ be a mapping of $A$ into $B$.

$f$ is a 1-1 mapping of $A$ into $B$ provided that $f(x_1)\neq f(x_2)$ whenever $x_1\neq x_2$, $x_1\in A$, $x_2\in A$.