7Daskin, M. A maximum expected coveting location mod- el: formulation, properties and heuristic solutions I-J] . Transportation Science, 1983 (1).
8Woodyatt, L R., Stott, K.L, Wolf, F.E. andVasko, F.J. An application combining set covering and fuzzy sets to optimally assign metallurgical grades to customer orders I-J] . Fuzzy Sets and Systems, 1993 (1).