Aminov, Yu. A. “On 2-Dimensional Surfaces in 3-Dimensional and 4-Dimensional Euclidean spaces. Results and Unsolved Problems”. Ukrains’kyi Matematychnyi Zhurnal 71, no. 1 (January 25, 2019): 3-36. Accessed April 19, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/1416.