[1] KИГУРАДЗЕ И. T.: 
К вопросу колеблемости решений нелинейных дифференциальных уравнений. Дифф. уравнения 8, 1965, 999-1006. 
Zbl 0314.35045 
[2] KUSANO T., ONOSE H.: 
Oscillation of Solutions of Nonlinear Differential Delay Equations of Arbitrary Order. Hiroshima Math. J. 1, 1972,  1-13. 
MR 0324175 | 
Zbl 0269.34064 
[3] LADAS G.: 
Oscillation and Asymptotic Behavior of Solutions of Differential Equations with Retarded Argument. J. diff. Equations 10, 1971, 281-290. 
MR 0291590 | 
Zbl 0216.12002 
[4] LIČKO I., ŠVEC M.: 
Le caractére oscillatoire des solutions de l'équation $y^{(n)}+f(x)y^{\alpha }=0$, $n>1$. Czech. Math. J. 13, 1963, 481-491. 
MR 0161001 
[5] MARUŠIAK P.: Note on the Ladas Paper on Oscillation and Asymptotic Behavior of Solutions of Differential Equations with Retarded Argument. J. diff. Equation 1, 1973, 450-456.
[6] MARUŠIAK P.: 
Oscillation of Solutions of the Delay Differential Equation $y^{(2n)}(t)+\sum^m_{i=1}p_i(t) f_j(y[h_i(t)])=0$,\quad $n\geq 1$. Čas. Pěst. Mat. 1, 1974, 131-141. 
MR 0404810 
[7] ONOSE  H.: 
Some Oscillation Criteria for n-th Order Nonlinear Delay-Differential Equations. Hiroshima Math. J. 2, 1971, 171-176. 
MR 0312032 | 
Zbl 0282.34050 
[8] STAIKOS V. A., SFICAS Y. G.: 
Oscillatory and Asymptotic Behavior of Functional Differential Equations. J. diff. Equations 3, 1972, 426-437. 
MR 0330707 | 
Zbl 0247.34076 
[9] ШЕВЕЛО. В. Н., ВАРЕХ И. В.: 
О некоторых свойствах решний дифференциальных уравнений с запаздыванием. Укр. Мат. Ж. 6, 1972, 807-813. 
Zbl 1156.34335