Petrus R, Jameel G. The existence and convergence of the periodic solution of the system of complementary equations - nonlinear differential of the second class type Volterra. EDUSJ [Internet]. 2006 Jan. 1 [cited 2025 Aug. 6];18(1):124-37. Available from: https://ojs.uomosul.edu.iq/index.php/edusj/article/view/23424