BOROK, V. M.; KENGNE, E. Classification of nonlocal boundary-value problems on a narrow strip. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 46, n. 4, p. 338–346, 1994. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5730. Acesso em: 15 dec. 2025.