KOPACH, M.I.; OBSHTA, A.F.; SHUVAR, B.A. Both-side approximation of solutions of differential equations. Carpathian Mathematical Publications, [S. l.], v. 1, n. 2, p. 172–179, 2009. Disponível em: https://personnel.pnu.edu.ua/index.php/cmp/article/view/4012. Acesso em: 18 jan. 2025.