Periodic Solutions For Nonlinear Systems of Multiple Integro-differential Equations that Contain Symmetric Matrices with Impulsive Actions. Iraqi Journal of Science [Internet]. 2023 Jan. 30 [cited 2024 Jul. 3];64(1):304-2. Available from: https://ijs.uobaghdad.edu.iq/index.php/eijs/article/view/5592