MENTYNSKYI, S. M.; SHUVAR, B. A. Two-Sided Approximation of Solutions of Boundary-Value Problems. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 57, n. 2, p. 284–288, 2005. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3597. Acesso em: 5 dec. 2025.