The Texas Consolidated Electronics Company is considering an R&D program encompassing eight research projects. In the model for this problem Xi is a 0-1 variable for the selection of project i, where i = 1 to 8. One of the conditions in the model is that the same decision be applied to project 2 and project 5. If project 2 is selected then project 5 is selected. And if project 2 is not selected then project 5 is not selected. This condition is represented by the following constraint