Oscillation theorems for second order neutral differential equations

The aim of this paper is to study the oscillation of the second order neutral differential equations  r(t) [x(t) + p(t)x(τ (t))]′′ + q(t)x(σ (t)) = 0. (E) The obtained results are based on the new comparison theorems, that enable us to reduce the problem of the oscillation of the second order equation to the oscillation of the first order equation. The obtained comparison principles essentially simplify the examination of the studied equations.