1. Mémoire sur les équations différentielles linéaires du second ordere;Sturm;J. Math. Pures Appl.,1836
2. Untersuchungen uber die reelen Nullstellen der Integrale lineare Differentialgleichungen;Kneser;Math. Ann.,1893
3. Oscillation and asymptotic behavior of solutions of nth order nonlinear delay differential equations;Mahfoud;J. Differential Equations,1977
4. Properties A and B of nth order linear differential equations with deviating argument;Koplatadze;Georgian Math. J.,1999
5. Comparison theorems for functional differential equations with deviating arguments;Kusano;J. Math. Soc. Japan,1981