Zhenguo Luo, Liping Luo & Yunhui Zeng. (1970). Oscillation Results for BVPs of Even Order Nonlinear Neutral Partial Differential Equations.
            <i>Journal of Nonlinear Modeling and Analysis</i>. <i>1</i> (2).
            261-270.
         doi:10.12150/jnma.2019.261