\begin{section}{Arrow}
The identity operator on $V$ is $\identity{V}$. The composition of
$f$ and $g$ is $\compose{f}{g}$. The inverse of $f$ is
- $\inverse{f}$.
+ $\inverse{f}$. If $f$ is a function and $A$ is a subset of its
+ domain, then the preimage under $f$ of $A$ is $\preimage{f}{A}$.
\end{section}
\begin{section}{Common}