Wongvisarut Khuangsatung and  Pakkinee Chitsakul,  Some Geodesics in Open Surfaces Classified by Clairaut's Relation.   journal   = {International Journal of Mathematical and Computational Sciences}, [online]. World Academy of Science, Engineering and Technology.
    September 2012, vol. 69(9). 1360 - 1364
    [viewed 23 April 2024]. Available from: https://publications.waset.org/pdf/8123.