Asymptotic solution of definite class of singularly perturbed linear boundary-value problems for ordinary differential equations. Annual of Sofia University St. Kliment Ohridski. Faculty of Mathematics and Informatics, [S. l.], v. 91, p. 79–95, 1999. Disponível em: https://annual.uni-sofia.bg/index.php/fmi/article/view/271. Acesso em: 11 jan. 2026.