ALIEV, I. V. Summability of series in the root functions of boundary-value problems of Bitsadze-Samarskii type. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 60, n. 4, p. 443–452, 2008. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3167. Acesso em: 6 dec. 2025.