STOROZH, O. G. Extremal expansions of the non-negative operator and accretive boundary problems . Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 42, n. 6, p. 858–860, 1990. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/8854. Acesso em: 6 dec. 2025.