LOVEIKIN, Yu. V.; PARASYUK, I. O. Invariant tori of locally Hamiltonian systems close to conditionally integrable systems. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 59, n. 1, p. 71–98, 2007. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3292. Acesso em: 6 dec. 2025.