BANG, Nguyen Thanh. On the observable conditions in the nonlinear systems. <b>Vietnam Journal of Mechanics</b>, Hanoi, Vietnam, v. 1, n. 1-2, p. 9–19, 1979. DOI: 10.15625/0866-7136/9888. Disponível em: https://vjmech.vast.vn/vjmech/article/view/9888. Acesso em: 9 nov. 2025.