Abstract
Consider the first-order linear delay differential equation xʹ(t) + p(t)x(τ(t)) = 0, t≥ t<sub>0</sub>, (1) where p, τ ∈ C ([t<sub>0</sub>,∞, ℝ<sup>+</sup>, τ(t) is nondecreasing, τ(t) < t for t ≥ t<sup>0</sup> and lim<sub>t→∞</sub> τ(t) = ∞, and the (discrete analogue) difference equation Δx(n) + p(n)x(τ(n)) = 0, n= 0, 1, 2,…, (1)ʹ where Δx(n) = x(n + 1) − x(n), p(n) is a sequence of nonnegative real numbers and τ(n) is a nondecreasing sequence of integers such that τ(n) ≤ n − 1 for all n ≥ 0 and lim<sub>n→∞</sub> τ(n) = ∞. Optimal conditions for the oscillation of all solutions to the above equations are presented.