Marziyeh Halimi and Roushanak Lotfikar and Simin Mansouri Borojeni,  Solving of the Fourth Order Differential Equations with the Neumann Problem.   journal   = {International Journal of Mathematical and Computational Sciences}, [online]. World Academy of Science, Engineering and Technology.
    October 2011, vol. 58(10). 1647 - 1649
    [viewed 20 April 2021]. Available from: https://publications.waset.org/pdf/7492.