H. A. . Mohamad and A. Jaddoa, “Asymptotic Criteria of Neutral Differential Equations with Positive and Negative Coefficients and Impulsive Integral Term”, Iraqi Journal of Science, vol. 61, no. 9, pp. 2315–2323, Sep. 2020, doi: 10.24996/ijs.2020.61.9.18.