SUN, He-Jun. Inequalities for Eigenvalues of a System of Higher-Order Differential Equations. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 66, n. 3, p. 394–403, 2014. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/2141. Acesso em: 5 dec. 2025.