Rosen Nikolaev, D. Zhelyazkova, T. Milkova. "MINIMIZING THE TRANSPORTATION COSTS BY MEANS OF THREE DIMENSIONAL TRANSPORTATION PROBLEM." 5th International Multidisciplinary Scientific Conference on Social Sciences and Arts SGEM 2018 (2018): 549-556. https://doi.org/10.5593/sgemsocial2018/1.4/S04.071