SHOVKOPLYAS, V. N. A criterion for the solvability of A linear boundary-value problem for A system of the second order. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 52, n. 6, p. 861–864, 2000. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/4484. Acesso em: 17 apr. 2025.