BARANOVICH, A. M.; DALETSKII, Yu. L. Some geometric-differential models in the class of formal operator power series. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 48, n. 6, p. 739–746, 1996. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5274. Acesso em: 17 apr. 2025.