BASKAKOV, A. G. On the reducibility of linear differential operators with unbounded operator coefficients. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 45, n. 5, p. 587–595, 1993. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5847. Acesso em: 27 apr. 2025.