Ashurov S. В. Equivalence of a part of derivatives of chains in the boundary value problems for the second-order ordinary differential equations . Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 44, n. 8, p. 1003–1011, 1992. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/8028. Acesso em: 5 dec. 2025.