CHENG SS. LYAPUNOV INEQUALITY FOR SYSTEM DISCONJUGACY OF EVEN ORDER DIFFERENTIAL EQUATIONS. Tamkang J. Math. [Internet]. 1991 Jun. 1 [cited 2024 Jul. 3];22(2):193-7. Available from: https://journals.math.tku.edu.tw/index.php/TKJM/article/view/4598