Oscillation and Asymptotic Behavior of Solutions of Nth Order Nonlinear Delay Differential Equations*

where n >, 2, a: [0, 00) + [0, a~), q: [0, co) --+ (-00, co), andf: (--co, 03) + (-00, CQ). We assume a(l), q(t), andf( x are continuous, q(t) < t for all t > 0, q(t) 3 co ) as t ---f co, and xf(x) > 0 for x # 0. Usually, a condition of monotonicity on f is needed in order to obtain results for Eq. (1) analogous to those of an ordinary differential equation of the same type. Many authors observed that such a monotonicity condition makes it possible to extend many results from an ordinary differential equation of type (1) to delay equations of type