YAKUBOVICH, V. A. On M. G. Krein’s work in the theory of linear periodic Hamiltonian systems. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 46, n. 1-2, p. 128–144, 1994. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5774. Acesso em: 6 dec. 2025.