Nisha Goyal and  R.K. Gupta,  On Symmetries and Exact Solutions of Einstein Vacuum Equations for Axially Symmetric Gravitational Fields.   journal   = {International Journal of Mathematical and Computational Sciences}, [online]. World Academy of Science, Engineering and Technology.
    August 2012, vol. 68(8). 838 - 841
    [viewed 11 May 2024]. Available from: https://publications.waset.org/pdf/14108.