Duong, A. T., and T. L. Tran. “Global Exponential Stability of a Class of Neural Networks With Unbounded Delays”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 60, no. 10, Oct. 2008, pp. 1401–1413, https://umj.imath.kiev.ua/index.php/umj/article/view/3254.