[1] CHANTURIA T. A.: Integral conditions of oscillation of solutions of higher-order linear differential equations. (Russian). Differencialnye Uravnenija, 16, 1980, 470-482.
[2] KIGURADZE I. T.: 
On the oscillatory and monotone solutions of ordinary differential equations. Arch. Math., 14, 1978, 21-44. 
MR 0512742 | 
Zbl 0408.34033[3] IVANOV A. F., KUSANO T., ŠEVELO V. N.: Comparison theorems for functional differential equations. (Russian). Inst. Math. Ukrain. Academy Sciences, 1984.
[4] OHRISKA J.: 
Oscillation of second-order delay and ordinary differential equation. Czech. Math. J., 34, 1984, 107-112. 
MR 0731983 | 
Zbl 0543.34054[5] OLÁH R.: 
Oscillation of linear retarded differential equation. Czech. Math. J., 34, 1984, 371-377. 
MR 0761419[6] PHILOS, Ch. G., SFICAS Y. G.: 
Oscillatory and asymptotic behaviour of second and third order retarded differential equations. Czech. Math. J., 32, 1982, 169-182. 
MR 0654054[7] WERBOWSKI J.: 
Oscillations of first-order differential inequalities with deviating arguments. Ann. Matem. purae et applic., CXL, 1985, 383-392. 
MR 0807646 | 
Zbl 0586.34058