Aminov, Yu. A. “On 2-Dimensional Surfaces in 3-Dimensional and 4-Dimensional Euclidean Spaces. Results and Unsolved Problems”. Ukrains’kyi Matematychnyi Zhurnal, vol. 71, no. 1, Jan. 2019, pp. 3-36, https://umj.imath.kiev.ua/index.php/umj/article/view/1416.