1. Driver, R. D., Runctional Differential Equations, Lecture notes at the University of Rhode Island, R.I., Summer 1970.
2. “Functional Differential Equations,”;Hale,1971
3. On the solutions of a linear homogeneous second order differential equation of the unstable type with retarded argument (Russian);Kamenskii;Trudy Sem. Teor. Differencial. Uravnenii s otklon. Arugmentom Univ. Druzby Narodov Patrisa Lumumby,1963
4. The functional-differential equation y'(x) = ay(λx)+by(s);Kato;Bull. Amer. Math. Soc.,1971
5. Oscillation and asymptotic behavior of solutions of differential equations with retarded argument;Ladas;J. Differential Equations,1971