T. T. Sang, N. Minh Thu, T. Hoang Khoi, N. Thi Kim Huong, L. T. N. Lan, and N. Van Thanh, “The Optimization of Transportation Costs in Logistics Enterprises during the Covid-19 Pandemic”, ARRUS J. Math. App. Sci., vol. 1, no. 2, pp. 62–71, Sep. 2021.