Webster, R. “On the Bohr-Mollerup-Artin Characterization of the Gamma Function”. Rev. Anal. Numér. Théor. Approx., vol. 26, no. 1, Aug. 1997, pp. 249-58, https://ictp.acad.ro/jnaat/journal/article/view/1997-vol26-nos1-2-art33.