Dries R. Goossens A. J. T. Maas Frits C. R. Spieksma Joris van de Klundert Exact algorithms for procurement problems under a total quantity discount structure. 603-626 2007 178 Eur. J. Oper. Res. 2 https://doi.org/10.1016/j.ejor.2006.03.010 db/journals/eor/eor178.html#GoossensMSK07