KALLEL, N.; Timoumi М. Subharmonics of a Nonconvex Noncoercive Hamiltonian System. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 55, n. 11, p. 1459–1466, 2003. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/4016. Acesso em: 6 dec. 2025.