KOSYAK, O. V.; NIZHNIK, L. P. Operators of Generalized Translation and Hypergroups Constructed from Self-Adjoint Differential Operators. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 57, n. 5, p. 659–668, 2005. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3632. Acesso em: 5 dec. 2025.