ВarkovskyV. V., and RoitbergY. A. “On the Minimum and Maximum Operator Corresponding to the General Elliptical Problem With Inhomogeneous Boundary Value Conditions ”. Ukrains’kyi Matematychnyi Zhurnal 18, no. 2 (March 5, 1966): 91-97. Accessed November 24, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/8719.