ORIDOROGA, L. L.; MALAMUD, M. M.; AGIBALOVA, A. V. On the completeness of general boundary value problems for $2 \times 2$ first-order systems of ordinary differential equations. Methods of Functional Analysis and Topology, [S. l.], v. 18, n. 1, p. 4–18, 2012. Disponível em: https://zen.imath.kiev.ua/index.php/mfat/article/view/502. Acesso em: 4 feb. 2026.