Вarkovsky V. V.; ROITBERG, Y. A. On the minimum and maximum operator corresponding to the general elliptical problem with inhomogeneous boundary value conditions . Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 18, n. 2, p. 91–97, 1966. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/8719. Acesso em: 6 dec. 2025.