1. C. Corduneanu. Integral Equations and Stability of Systems. Academic Press, New York, 1973.
2. W.S.C. Gurney, S.P. Blythe and R.M. Nisbet. Nicholson's Blowflies Revisited.Nature, 1980, 287: 17–20.
3. Li Senlin and Wen Lizhi. Functional-differential Equations. Hunan Press of Science and Technology, Changsha, 1986, p.120 (in Chinese).
4. T. Yoshizawa. Stability Theory by Lyapunov Second Method. The Mathematical Society of Japan, 1966.
5. K. Gopalsamy. Globally Asymptotical Stability in a Periodic Integrodifferential System.Tohoku Mathematical Journal, 2nd Ser., 1985, 3: 323–332.