Sameerah Jamal and  Abdul Hamid Kara and  Ashfaque H. Bokhari,  Symmetries, Conservation Laws and Reduction of Wave and Gordon-type Equations on Riemannian Manifolds.   journal   = {International Journal of Mathematical and Computational Sciences}, [online]. World Academy of Science, Engineering and Technology.
    December 2011, vol. 60(12). 2105 - 2108
    [viewed 24 May 2022]. Available from: https://publications.waset.org/pdf/9539.