DERKACH , V. A.; MALAMUD , M. M. Characteristic functions of almost soluble expansion of the Hermitian operators . Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 44, n. 4, p. 435–459, 1992. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/7885. Acesso em: 6 dec. 2025.