1. A. Zahariev and D. Bainov, ?Oscillating properties of the solutions of a class of neutral type functional differential equations,? Bull. Austral. Math. Soc.,22, 365?382 (1980).
2. S. Grace and B. Lalli, ?Oscillations of nonlinear second order neutral delay differential equations,? Radovi Math.,3, 77?84 (1987).
3. M. Grammatikopoulos, G. Ladas, and A. Meimardiou, ?Oscillations of second order neutral delay differential equations,? Radovi Math.,1, 267?274 (1985).
4. M. Grammatikopoulos, G. Ladas, and Y. Sficas, ?Oscillation and asymptotic behavior of neutral equations with variable coefficients,? Radovi Math.,2, 279?303 (1986).
5. E. Grove, M. Kulenovic, and G. Ladas, ?Sufficient conditions for oscillation and nonoscillation of neutral equations,? J. Different. Equat.,68, 373?382 (1987).