Aliev, B. A. 2010. “Solvability of the Boundary-Value Problem for the Second-Order Elliptic Differential-Operator Equation With Spectral Parameter in the Equation and Boundary Conditions”. Ukrains’kyi Matematychnyi Zhurnal 62 (1), 3 - 14. https://umj.imath.kiev.ua/index.php/umj/article/view/2839.