Ardjouni, Abdelouaheb, and Ahcene Djoudi. “Existence of Positive Periodic Solutions for Two Types of Second-Order Nonlinear Neutral Differential Equations With Variable Delay”. Proyecciones (Antofagasta, On line) 32, no. 4 (1): 377-391. Accessed April 18, 2024. https://www.revistaproyecciones.cl/index.php/proyecciones/article/view/1304.