“Stability of Minimal Surfaces in the Sub-Riemannian Manifold $\widetilde{E(2)}$”. Visnyk of V. N. Karazin Kharkiv National University. Ser. Mathematics, Applied Mathematics and Mechanics, vol. 98, Dec. 2023, pp. 50-67, https://doi.org/10.26565/2221-5646-2023-98-04.