[1] T. A. Čanturia: On specific criteria of oscillation of solutions of linear differential equations with retarded argument. Ukrajin. Mat. Žurn. 38 (1986), 662-665 (Russian). MR 0870376

[2] J. Jaroš: Necessary and sufficient conditions for oscillations of first order delay differential equations and inequalities. submitted for publication.

[3] I. T. Kiguradze: On the oscillation of solutions of the equation $\frac{d^m u}{dt^m} + a(t) |u|^n sgn u = 0$. Mat. Sb. 65 (1964), 172-187 (Russian). MR 0173060 | Zbl 0135.14302

[4] R. G. Koplatadze, T. A. Čanturia: "On oscillatory properties of differential equations with deviating arguments". Tbilisi Univ. Press, Tbilisi, 1977 (Russian).

[5] T. Kusano: On even order functional differential equations with advanced and retarded arguments. J. Differential Equations 45 (1982), 75-84. DOI 10.1016/0022-0396(82)90055-9 | MR 0662487

[6] G. Ladas, I. P. Stavroulakis: On delay differential inequalities of higher order. Canad. Math. Bull. 25 (1982), 348-354. DOI 10.4153/CMB-1982-049-8 | MR 0668953

[7] G. Ladas Y. G. Sficas, I. P. Stavroulakis: Necessary and sufficient conditions for oscillations. Amer. Math. Monthly 90 (1983), 637-640. DOI 10.1080/00029890.1983.11971299 | MR 0719755

[8] G. Ladas Y. G. Sficas, I. P. Stavroulakis: Necessary and sufficient conditions for oscillations of higher order delay differential equations. Trans. Amer. Math. Soc. 285 (1984), 81-90. DOI 10.1090/S0002-9947-1984-0748831-8 | MR 0748831

[9] G. Ladas, I. P. Stavroulakis: Oscilations of differential equations of the mixed type. J. Math. Phys. Sciences 18 (1984), 245-262. MR 0811966

[10] V. A. Nadareišvili: On oscillatory and monotonic solutions of first order differential equations with retarded arguments. Reports of Enlarged Sessions of the Seminar of I. N. Vekua Institute of Applied Mathematics 1 (1985), 111-115 (Russian).

[11] Ch. G. Philos: On the existence of nonoscillatory solutions tending to zero at $\infty$ for differential equations with positive delays. Arch. Math. 36 (1981), 168-178. DOI 10.1007/BF01223686 | MR 0619435