 Then it holds that 

formula_36, where formula_37 for each formula_38.On the other hand, Steinberg has shown that the height of an optimal solution can be upper bounded by 

formula_39

More precisely he showed that given a formula_40 and a formula_41 then the items formula_7 can be placed inside a box with width formula_43 and height formula_44 if

formula_45, where formula_37.Since this problem is NP-hard, approximation algorithms have been studied for this problem.