Juan Zhang and  Changzhao Li,  Characterization of Solutions of Nonsmooth Variational Problems and Duality.   journal   = {International Journal of Mathematical and Computational Sciences}, [online]. World Academy of Science, Engineering and Technology.
    September 2013, vol. 73(1). 112 - 118
    [viewed 19 April 2024]. Available from: https://publications.waset.org/pdf/16970.