Bai, Yongzhen, Yannan Li, and Youyu Wang. 2013. “Lyapunov-Type Inequalities for Quasilinear Systems With Antiperiodic Boundary Conditions”. Ukrains’kyi Matematychnyi Zhurnal 65 (12), 1646–1656. https://umj.imath.kiev.ua/index.php/umj/article/view/2543.