OSTROVSKII, V. L.; SAMOILENKO, Yu. S. On pairs of unbounded self-adjoint operators satisfying an algebraic relation. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 45, n. 9, p. 1253–1258, 1993. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5927. Acesso em: 5 dec. 2025.