Derivative of Cotangent of Function

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

Then:
 * $\map {\dfrac \d {\d x} } {\cot u} = -\csc^2 u \dfrac {\d u} {\d x}$

where $\cot$ is the cotangent function and $\csc$ is the cosecant function.