The Texas Consolidated Electronics Company is considering an R&D program encompassing eight research projects.

In the model for this problem $x_i$ 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:

$x_2+x_5=1$

$x_2=x_5$

$x_{2}36$

$x_2{x}_5$