PARHI, N.; CHAND, S. Oscillation of Second Order Neutral Delay Differential Equations With Positive and Negative Coefficients. The Journal of the Indian Mathematical Society, [S. l.], v. 66, n. 1-4, p. 227–235, 1999. Disponível em: http://www.informaticsjournals.com/index.php/jims/article/view/22006. Acesso em: 9 may. 2024.