/* Objective function */
min:   xab +   xac + 9 xbc + 2 xbd + 3 xce + 2 xda + 6 xdc + 8 xde;

/* Variable bounds */

     - xab -   xac                         +   xda                  = -5;
       xab         -   xbc -   xbd                                  = -7;
               xac +   xbc         -   xce         +   xdc          =  8;
                               xbd         -   xda -   xdc -   xde  = -5;
                                       xce                 +   xde  =  9;