1.
Adel Aziz M, Butris R. The existence and approximation of the periodic solutions for system of second order nonlinear differential equationsby using Lebesgue integrable. EDUSJ [Internet]. 2007 Jun. 1 [cited 2025 Aug. 4];19(4):80-106. Available from: https://rjps.uomosul.edu.iq/index.php/edusj/article/view/18354