private List<Integer> extractParticipients(Assignment a) {
   List<Integer> participients = new ArrayList<>(a.assignedVariables());
   Collections.sort(participients);
   return participients;
 }
 public List<KAryConstraint> collectAllSubConstraints(Assignment a) {
   LinkedList<KAryConstraint> ret = new LinkedList<>();
   _collectAllSubConstraints(a.assignedVariables(), ret);
   return ret;
 }