For a neutral differential equation with positive and changeable sign coefficients , oscillation criteria are established, where q(t) is not required as nonnegative. Several new results are obtained.
Weiping Yan. Jurang Yan. "Conditions for Oscillation of a Neutral Differential Equation." Int. J. Differ. Equ. 2010 (SI2) 1 - 7, 2010. https://doi.org/10.1155/2010/354726