OSCILLATION CRITERIA FOR HIGHER-ORDER FUNCTIONAL DIFFERENTIAL EQUATION OF MIXED TYPE

<正> In this paper we discuss the oscillation of solutions of the following difference-differential equation of the higher orderwhere Pi,τi,qi,σj are constants, the deviating arguments τi,σi may be either positive or negative, qi,…qm have the same sign. We show that the necessary and sufficient condition for all solutions of the above equation to be oscillatory is the associated characteristic equation having no real roots.