A
D5722: Random positive real number $X \in \text{Random}(0, \infty)$ is a
gamma random positive real number with parameters $\alpha, \beta \in (0, \infty)$ if and only if
\begin{equation}
\forall \, t \in \mathbb{R} :
\mathbb{E} (e^{i t X})
= \frac{1}{\left( 1 - \frac{i t}{\beta} \right)^{\alpha}}
\end{equation}