Li Xiguang,  Positive Solutions for Boundary Value Problems of Fourth-Order Nonlinear Singular Differential Equations in Banach Space.   journal   = {International Journal of Mathematical and Computational Sciences}, [online]. World Academy of Science, Engineering and Technology.
    September 2013, vol. 76(4). 762 - 766
    [viewed 05 May 2024]. Available from: https://publications.waset.org/pdf/17068.