public Interdependence getDependenceAt(int idx) {
   Interdependence intdep = (Interdependence) interdependencies.get(idx);
   // just checking -- may remove if not needed
   if (intdep.getPolicyPosition() != idx) {
     System.err.println("error: policy position and index do not match");
     System.exit(0);
   }
   return intdep;
 }
 public void print() {
   System.out.println("size: " + interdependencies.size());
   for (Interdependence ind : interdependencies) {
     System.out.println(ind.toString());
   }
 }