KARANDJULOV, L. Asymptotic solution of definite class of singularly perturbed linear boundary-value problems for ordinary differential equations. Ann. Sofia Univ. Fac. Math. and Inf., [S. l.], v. 91, p. 79–95, 1999. Disponível em: https://stipendii.uni-sofia.bg/index.php/fmi/article/view/271. Acesso em: 4 dec. 2024.