Symокоп V. G.; TROFIMCHUK, E. P. On regularity of linear systems with a degenerate matrix by the derivative. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 45, n. 2, p. 279–286, 1993. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5810. Acesso em: 5 dec. 2025.