Kovalev, A.M., G.V. Gorr, and V.N. Nespirnyy. 2025. “Invariant Relations for Nonautonomous Systems of Differential Equations”. Reports of the National Academy of Sciences of Ukraine, no. 2 (March). Kyiv, Ukraine:13-19. https://doi.org/10.15407/dopovidi2014.02.013.