Orlov, I.V., E.V. Bozhonok, and E.M. Kuzmenko. 2025. “Necessary Conditions for the K-Extremum of a Variational Functional in Sobolev Spaces over Multi-Dimensional Domains”. Reports of the National Academy of Sciences of Ukraine, no. 4 (February). Kyiv, Ukraine:19-24. https://doi.org/10.15407/dopovidi2014.04.019.