PIPA, H. M.; STOROZH, O. G. On some perturbations changing the domain of proper extension of positively definite operator. Methods of Functional Analysis and Topology, [S. l.], v. 11, n. 3, p. 257–269, 2005. Disponível em: https://zen.imath.kiev.ua/index.php/mfat/article/view/284. Acesso em: 16 dec. 2025.