Derivative of Cosecant of Function

Theorem
Let $u$ be a differentiable real function of $x$.

Then:
 * $\map {\dfrac \d {\d x} } {\csc u} = \csc u \cot u \dfrac {\d u} {\d x}$

where $\sec$ is the cosecant function and $\tan$ is the cotangent function.