Copyright © 1991 Published by Elsevier Inc.
On the nature of the nonoscillatory solutions of a class of neutral delay differential equations
Received 8 August 1989.
Submitted by V. Lakshmikantham
Available online 30 June 2004.
Abstract
Consider the neutral delay differential equation
, (E) where p, q, τ, σ1, and σ2 are nonnegative constants. For τ
σ2, we prove that all nonoscillatory solutions of (E) are bounded if and only if: (C) The characteristic equation λ + pλe−λτ + q(e−λσ1 − e−λσ2) = 0 (*) of (E) has no positive roots and zero is a simple root if (*). We also prove that condition (C) is equivalent to 1 + p > q(σ1 − σ2) if τ
σ2. Moreover, for the case where τ > σ2, we show that (C) is a necessary and sufficient condition for every nonoscillatory solution x of (E) to be bounded or such that 





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(0, + ∞). (For the case
0, τ 



