PARASYUK, I. O.; SAMOILENKO, A. M. Nilpotent flows of S1-invariant Hamiltonian systems on 4-dimensional symplectic manifolds. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 49, n. 1, p. 122–140, 1997. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/4991. Acesso em: 5 dec. 2025.