Potapenko, I. V. “New Equations of Infinitesimal Deformations of Surfaces in $E_3$”.
Ukrains’kyi Matematychnyi Zhurnal
62, no. 2 (February 25, 2010): 199–202. Accessed April 27, 2025.
https://umj.imath.kiev.ua/index.php/umj/article/view/2856
.