Baranetskij, Ya.O., P.I. Kalenyuk, M.I. Kopach, and A.V. Solomko. 2019. “The Nonlocal Boundary Value Problem With Perturbations of Mixed Boundary Conditions for an Elliptic Equation With Constant Coefficients. I”. Carpathian Mathematical Publications 11 (2):228-39. https://doi.org/10.15330/cmp.11.2.228-239.