Sosnitskii, S. P. “On the Function of Hamiltonian Action for Nonholonomic Systems and Its Application to the Investigation of Stability”. Ukrains’kyi Matematychnyi Zhurnal 51, no. 10 (October 25, 1999): 1411–1416. Accessed April 11, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/4740.