SINGH, B. Asymptotic Nonoscillations in Fourth Order Retarded Differential Equations. The Journal of the Indian Mathematical Society, [S. l.], v. 40, n. 1-4, p. 53–67, 1976. Disponível em: http://informaticsjournals.com/index.php/jims/article/view/16613. Acesso em: 2 may. 2024.