YAKOVETS, V. P. On some properties of degenerate linear systems. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 49, n. 9, p. 1278–1296, 1997. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5127. Acesso em: 5 dec. 2025.