Regarding this problem formulation, first note that constraint (4.8) restricts the order quantity to a single truckload. Removing this constraint would significantly complicate the behavior of the combined ordering and transportation cost, and therefore, we choose instead to use the simpler formulation here. Also, via constraint (4.9), we restrict our solutions to those with non-negative safety stock. Finally, note that we have stated the fill rate constraint (4.10) both in terms of R (and not z) and in the form of a sum of functions of the decision variables (gathering the terms of this constraint slightly differently than we did in Chapter 3).