KHOMA, N. H. Existence of a smooth solution of one boundary-value problem. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 47, n. 12, p. 1717–1719, 1995. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5569. Acesso em: 5 dec. 2025.