a1 Department of Mathematics, University of Rhode Island, Kingston, R.I. 02881, USA.
a2 Department of Mathematics, University of Sarajevo, Sarajevo 71000, Yugoslavia.
a3 Department of Electrical Engineering, Democritus University of Thrace, Xanthi 67100, Greece.
Consider the neutral delay differential equation
where p R, τ ≥ 0, q1 > 0, σ1 ≥ 0, for i = 1, 2, …, k. We prove the following result.
Theorem. A necessary and sufficient condition for the oscillation of all solutions of Eq. (1) is that the characteristic equation
has no real roots.
(Received December 13 1985)