1. Stability and Periodic Solutions of Ordinary and Functional Differential Equations;Burton,1985
2. Upper and lower bounds for Liapunov functionals;Burton;Funkcial. Ekvac.,1989
3. Stability conditions for linear non-autonomous delay differential equations;Busenberg;Quart. Appl. Math.,1984
4. Theory of Functional Differential Equations;Hale,1977
5. Asymptotic stability for a differential–difference equation containing terms with and without a delay;Hatvani;Acta Sci. Math. (Szeged),1995