1.
N.Butris R, S.Seeto A. Existence of a Periodic Solution for Nonlinear Systems of Differential Equations with Retarded Argument. JES [Internet]. 2005 Jan. 1 [cited 2025 Sep. 10];17(1):10-6. Available from: https://edusj.uomosul.edu.iq/index.php/edusj/article/view/41953