[1] FOLTYNSKA I., WERBOWSKI J.: On the oscillatory behaviour of solutions of system of differential equations with deviating arguments. Colloquia Math. Soc. J. B. 30, Qualitative theory of Diff. Eq. Szeged, 1979, 243-256. MR 0680596

[2] KITAMURA Y., KUSANO T.: On the oscillation of a class of nonlinear differential systems with deviating argument. J. Math. Annal Appl. 66, 1978, 20-36. MR 0513483 | Zbl 0417.34107

[3] KITAMURA Y., KUSANO T.: Asymptotic properties of solutions of two-dimensional differential systems with deviating argument. Hiroshima Math. J. 2, 1978, 305-326. MR 0492742 | Zbl 0385.34043

[4] VARECH N. V., GRITSAI A. G., ŠEVELO V. N.: On the oscillation of solution of ceгtain systems of differential equations with retarded argument. Metody količestvennogo a kačestvennogo issledovanija diffeгenciaľnych i integraľnych uгavnenij, Kiev 1975, 20-38 (in Russian).

[5] VARECH N. V., ŠEVELO V. N.: On the conditions of the oscillation of the solutions of differential system with гetarded aгguments. Kačestvennye mеtody teorii differenciaľnych uravnenij s otkloniajuščimsia aгgumentom, Kiev 1977, 26-44 (in Russian).

[6] ŠEVELO V. N., VARECH N. V.: On some properties of solutions of system of functional differential equations. Kačestvennoe issledovanie differenciaľno-functionaľnych uгavnenij, Kiev, 1980, 153-171 (in Russian). MR 0612663