OSCILLATION CRITERIA OF FOURTH-ORDER NONLINEAR SEMI-NONCANONICAL NEUTRAL DIFFERENTIAL EQUATIONS VIA A CANONICAL TRANSFORM.

In this work first we transform the semi-noncanonical fourth order neutral delay differential equations into canonical type. This simplifies the investigations of finding the relationships between the solution and its companion function which plays an important role in the oscillation theory of neutral differential equations. Moreover, we improve these relationships based on the monotonic properties of positive solutions. We present new conditions for the oscillation of all solutions of the corresponding equation which improve the oscillation results already reported in the literature. Examples are provided to illustrate the importance of our main results. [ABSTRACT FROM AUTHOR]