BELIKOV , S. A. On observability of linear and bilinear systems of the Hilbert space. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 40, n. 2, p. 139–144, 1988. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/9108. Acesso em: 6 dec. 2025.