Pankaj Dutta and Debjani Chakraborty,  A Study on Linking Upward Substitution and Fuzzy Demands in the Newsboy-Type Problem .   journal   = {International Journal of Mathematical and Computational Sciences}, [online]. World Academy of Science, Engineering and Technology.
    January 2007, vol. 1(1). 113 - 118
    [viewed 25 April 2024]. Available from: https://publications.waset.org/pdf/5350.