A theorem on perturbation of coisotropic invariant tori of locally Hamiltonian systems, and its applications. Neliniini Kolyvannya, [S. l.], v. 8, n. 4, p. 490–515, 2005. Disponível em: https://twinhead.imath.kiev.ua/index.php/nosc/article/view/369. Acesso em: 22 jan. 2026.