GIAP, Tran Van. ON PERTURBATIONS OF SECOND ORDER AND THIRD ORDER EQUATIONS Periodica Polytechnica Mechanical Engineering, [S. l.], v. 18, n. 2-3, p. 87–94, 1974. Disponível em: https://pp.bme.hu/me/article/view/5987. Acesso em: 20 may. 2024.