[1]
A. M. Samoilenko and V. L. Kulik, “Concerning existence of the Lyapunov sign-variable functions for linear systems of differential equations”, Ukr. Mat. Zhurn., vol. 44, no. 1, pp. 100–106, Feb. 1992, Accessed: Apr. 13, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/7800