Zakharin, S. F., and I. O. Parasyuk. 1998. “Generalized and Classical Almost Periodic Solutions of Lagrangian Systems Convex on a Compact Set”.
Ukrains’kyi Matematychnyi Zhurnal 50 (12): 1601–1608.
https://umj.imath.kiev.ua/index.php/umj/article/view/4779.