Nikolaev, Rosen Nikolaev, Milkova, Tanka Vasileva, Zhelyazkova, Donka Dimitrova Minimizing the Transportation Costs by Optimal Positioning of Units in Logistics Systems,
STEF92 Technology Ltd., 2017, p. 509 - 516, ISBN 978-619-7408-16-4 ; ISSN 2367-5659.