AleksandrovichI. N. “Differential Operators Determining Solutions of Elliptic Equations”. Ukrains’kyi Matematychnyi Zhurnal 47, no. 12 (December 25, 1995): 1587–1592. Accessed October 6, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/5552.