“On Smoothness of Generalized Quasiperiodic Solutions of Lagrangian Systems on Riemannian Manifolds of Non-Positive Curvature”. Neliniini Kolyvannya 2, no. 2 (June 29, 1999): 180–193. Accessed January 22, 2026. https://twinhead.imath.kiev.ua/index.php/nosc/article/view/53.