BEKKER, M. B. On non-densely defined invariant Hermitian contractions. Methods of Functional Analysis and Topology, [S. l.], v. 13, n. 3, p. 223–235, 2007. Disponível em: https://zen.imath.kiev.ua/index.php/mfat/article/view/351. Acesso em: 16 dec. 2025.