Sverdan, M. L. 1996. “The Second Lyapunov Method for the Investigation of Stability of Differential Equations With Pulse Perturbations and Markov Coefficients”. Ukrains’kyi Matematychnyi Zhurnal 48 (6), 826-33. https://umj.imath.kiev.ua/index.php/umj/article/view/5282.