Parasyuk, I. O. “Quasiperiodic Extremals of Nonautonomous Lagrangian Systems on Riemannian Manifolds”. Ukrains’kyi Matematychnyi Zhurnal 66, no. 10 (October 25, 2014): 1387–1406. Accessed March 29, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/2230.