MathItems

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

If $E\subset A$, $f(E)$ is defined to be the set of all elements $f(x)$, for $x\in E$. We call $f(E)$ the image of $E$ under $f$.

If $f(A)=B$, we say that $f$ maps $A$ onto $B$.