1. Each unit is assigned a set of initial possible labels.

2. All relations are checked to see if some pairs of labels

    are impossible for certain pairs of units.

3.  Inconsistent labels are removed from the label sets.

4. If any labels have been filtered out

         then another pass is executed

         else the relaxation part is done.

5.  If there is more than one labeling left, a tree search

     can be used to find each of them.