TSVETKOV, E. L. Smoothness of generalized solutions of the third boundary-value problem for an elliptic differential-difference equation. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 45, n. 8, p. 1140–1150, 1993. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5911. Acesso em: 11 apr. 2025.