Assume you have 3 possible projects to invest in (represented by binary variables X1, X2 and X3). You know that if project 1 is selected, then project 2 must also be selected. Create a constraint that permits all allowed scenarios but does not permit all non-allowed scenarios (Hint: start by creating a "truth table"). O X2 - X1 =0 V \\X2 + X1 >= 0 X2 + X1