CHENG, SUI SUN. “LYAPUNOV INEQUALITY FOR SYSTEM DISCONJUGACY OF EVEN ORDER DIFFERENTIAL EQUATIONS”. Tamkang Journal of Mathematics 22, no. 2 (June 1, 1991): 193–197. Accessed July 3, 2024. https://journals.math.tku.edu.tw/index.php/TKJM/article/view/4598.