1. V. N, Shevelo, ?Some questions of the theory of oscillation of solutions of nonlinear nonautonomous differential equations,? Proc. Fourth Conf. Nonlinear Oscillations, Prague (1968),pp.251?256.
2. V. N. Shevelo, ?On the influence of the lag in the argument on the oscillatoriness of solutions of higher-order differential equations,? Proc, Fifth Internat. Conf. Nonlinear Oscillations [in Russian], Vol.2, Izd. Inst. Matematiki Akad. Nauk UkrSSR, Kiev (1970).
3. G. Ladas, ?Oscillation and asymptotic behavior of solutions of differential equations with retarded argument,? J. Different. Equat.,10, No.2, 281?290 (1971).
4. R. G. Koplatadze, ?On the oscillatoriness of solutions of second-order differential equations with lagging argument,? Soobshch. Akad. Nauk GruzSSR,60, No.2 (1970).
5. I. T. Mrugadze, ?On the oscillatoriness of solutions of the equation dmu/dtm +a(t) ¦u ¦nsign u= 0,? Matem. Sb.,65, No. 2 (1964).