NIZHNIK , L. P.; TARABORKIN , L. A. On self-conjugate operators generated nonhomogeneous elliptical problems with discontinuity boundary conditions and conditions of conjugacy. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 43, n. 3, p. 374–381, 1991. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/9618. Acesso em: 12 jan. 2026.