HRUSHKA, Ya. I. On the order of convergence of a semigroup to the identity operator. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 48, n. 6, p. 847–851, 1996. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5285. Acesso em: 14 apr. 2025.