KASHPIROVSKII, A. I.; MYTNIK, Yu. V. Approximation of solutions of operator-differential equations by operator polynomials. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 50, n. 11, p. 1506–1516, 1998. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/4802. Acesso em: 11 apr. 2025.