Mittag-Leffler Expansion for Hyperbolic Cotangent Function

Theorem

 * $\ds \pi \map \coth {\pi z} = \frac 1 z + 2 \sum_{n \mathop = 1}^\infty \frac z {z^2 + n^2}$

where:
 * $z \in \C$ is not an integer multiple of $i$
 * $\coth$ is the hyperbolic cotangent function.