Nonoscillatory differential equations with retarded and advanced arguments

Sufficient conditions are derived for a vector-matrix system of the form \[ \frac {{{d^n}X\left ( t \right )}}{{d{t^n}}} + {\left ( { - 1} \right )^{n - 1}}\left [ {P\left ( t \right )X\left ( {t - {\tau _1}\left ( t \right )} \right ) + Q\left ( t \right )X\left ( {t + {\tau _2}\left ( t \right )} \right )} \right ] = 0\] to be nonoscillatory.