KALIMBETOV, B.T.; HABIBULLAEV, Zh.O. Regularization method for singularly perturbed integro-differential systems with multiple spectrum. Bulletin of the Karaganda University. Mathematics Series, [S. l.], v. 80, n. 4, p. 91–97, 2015. Disponível em: https://mts.buketov.edu.kz/index.php/mathematics-vestnik/article/view/66. Acesso em: 10 jul. 2025.