Asymptotic method for the investigation of a weakly-linear system of four differential equations. Neliniini Kolyvannya, [S. l.], v. 2, n. 2, p. 267–277, 1999. Disponível em: https://twinhead.imath.kiev.ua/index.php/nosc/article/view/61. Acesso em: 22 jan. 2026.