SLYUSARCHUK, V. Yu. Equations in a Hilbert space whose solution sets are invariant with respect to a group isomorphic to a one-parameter group of unitary operators. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 72, n. 1, p. 86–99, 2020. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/687. Acesso em: 7 apr. 2025.