Martynyuk, A. A., and C.- tsi Sun’. “On the Practical $μ$-Stability of Solutions of Standard Systems With Delay”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 51, no. 2, Feb. 1999, pp. 204–213, https://umj.imath.kiev.ua/index.php/umj/article/view/4599.