BaranovichA. M., and DaletskiiYu. L. “Some Geometric-Differential Models in the Class of Formal Operator Power Series”. Ukrains’kyi Matematychnyi Zhurnal 48, no. 6 (June 25, 1996): 739-746. Accessed November 24, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/5274.