ZakharinS. F., and ParasyukI. O. “Generalized and Classical Almost Periodic Solutions of Lagrangian Systems Convex on a Compact Set”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 50, no. 12, Dec. 1998, pp. 1601–1608, https://umj.imath.kiev.ua/index.php/umj/article/view/4779.