VALITSKII, Yu. N.; GOLETS, B. I.; ZELENYAK, T. I. Multipoint Boundary Conditions for Differential Operators. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 55, n. 1, p. 126–131, 2003. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3894. Acesso em: 6 dec. 2025.