Zagirnyak, Valentina, Boris Nevzlin, and Veronika Zahorulko. “DETERMINATION OF THE CONDITIONS FOR THE EXISTENCE OF HIGHER-ORDER DIFFERENTIAL ELECTROMAGNETIC INVARIANTS”. Journal of Energy Technology 8, no. 2 (May 22, 2024): 11–16. Accessed February 26, 2026. https://old.journals.um.si/index.php/jet/article/view/4395.