Leiko, S. G., and Yu. S. Fedchenko. 2003. “Infinitesimal Rotary Deformations of Surfaces and Their Application to the Theory of Elastic Shells”. Ukrains’kyi Matematychnyi Zhurnal 55 (12): 1697-1703. https://umj.imath.kiev.ua/index.php/umj/article/view/4031.