1. Myshkis A.D., “On solutions of linear homogeneous differential equations of the second order of periodic type with a retarded argument,” Mat. Sb., vol. 28, no. 3, 641–658 (1951).
2. Azbelev N.V. and Simonov P.M., Stability of Differential Equations with Aftereffect, Taylor and Francis, London (2002).
3. Yorke J.A., “Asymptotic stability for one dimensional differential-delay equations,” J. Differ. Equ., vol. 7, 189–202 (1970).
4. Amemiya T., “On the delay-independent stability of a delayed differential equation of $ 1 $st order,” J. Math. Anal. Appl., vol. 142, no. 1, 13–25 (1989).
5. Malygina V.V., “Stability of solutions of some linear differential equations with aftereffect,” Russian Math. (Iz. VUZ. Matematika), vol. 37, no. 5, 63–75 (1993).