Helen L. Hein and  Joachim Schwarte,  Products in Early Development Phases: Ecological Classification and Evaluation Using an Interval Arithmetic Based Calculation Approach.   journal   = {International Journal of Energy and Environmental Engineering}, [online]. World Academy of Science, Engineering and Technology.
    April 2019, vol. 149(5). 368 - 374
    [viewed 15 November 2019]. Available from: https://publications.waset.org/pdf/10010386.