Y. S. Fedchenko, “Normal and tangential geodesic deformations of the surfaces of revolution”, Ukr. Mat. Zhurn., vol. 61, no. 10, pp. 1396–1402, Oct. 2009, Accessed: Apr. 13, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/3109