Before revision:   Using the Selection problem as an example , we show that it is possible to produce instances which are ten times as hard to solve on average for a state-of-the-art mixed-integer programming solver  .
After revision:  Our approach does not make any assumptions on the problem structure and can thus be applied to any combinatorial problem. Using the Selection problem as an example , we show that it is possible to produce instances which are ten times as hard to solve on average for a state-of-the-art mixed-integer programming solver .