ADAMYAN, V. M. Non-negative perturbations of non-negative self-adjoint operators. Methods of Functional Analysis and Topology, [S. l.], v. 13, n. 2, p. 103–109, 2007. Disponível em: https://zen.imath.kiev.ua/index.php/mfat/article/view/342. Acesso em: 16 dec. 2025.