Nguyen Van Dao. “Investigation of Motion Stability in a Critical Case by the Asymptotic Method of Non-Linear Mechanics ”. Ukrains’kyi Matematychnyi Zhurnal 23, no. 4 (June 29, 1971): 545–552. Accessed December 6, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/8591.