Product of r Choose m with m Choose k/Complex Numbers

Theorem
For all $z, w \in \C$ such that it is not the case that $z$ is a negative integer and $t, w$ integers:
 * $\dbinom z t \dbinom t w = \dbinom z w \dbinom {z - w} {t - w}$

where $\dbinom z w$ is a binomial coefficient.