Holub, A. P., and L. O. Chernetska. “Two-Dimensional Generalized Moment Representations and Padé Approximations for Some Humbert Series”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 65, no. 10, Oct. 2013, pp. 1315–1331, https://umj.imath.kiev.ua/index.php/umj/article/view/2511.