1. N.V.Azbelev, About distribution of zeros of the second order differential equation with delayed argument. (Russian)Differentsial'nye Uravneniya 7(1971), No. 7, 1147–1157; English translation:Differential Equations 7(1971)
2. N.V.Azbelev and A.I.Domoshnitsky, A question concerning linear differential inequalities, II. (Russian)Differentsial'nye Uravneniya 27(1991), No. 6, 923–931; English translation:Differential Equations 27(1991), 641–647.
3. A.I.Domoshnitsky, Extension of Sturm's theorem to apply to an equation with time-lag. (Russian)Differentsial'nye Uravneniya 19(1983), No. 9, 1475–1482; English translation:Differential Equations 19(1983), 1099–1105.
4. Yu.I.Domshlak, Sturmian comparison method in investigation of behavior of solutions for differential-operator equations. (Russian) “Elm,”Baku, 1986.
5. Yu.I.Domshlak, Sturmian comparison theorem for first and second order differential equations with mixed delay of argument. (Russian)Ukrain. Mat. Zh. 34(1982), No. 2, 158–163; English translation:Ukrainian Math. J. 34(1982).