HASSAN MAHMOOD, A.; أکرم. Investigation of solvability conditions of certain boundary value problem by perturbation method. Journal of Education and Science (JES), [S. l.], v. 23, n. 1, p. 54–63, 2010. DOI: 10.33899/edusj.2010.57976. Disponível em: https://rjps.uomosul.edu.iq/index.php/edusj/article/view/18048. Acesso em: 4 aug. 2025.