@Override
  public synchronized void addInReference(RefElement refElement) {
    List<RefElement> inReferences = myInReferences;
    if (inReferences == null) {
      myInReferences = inReferences = new ArrayList<>(1);
    }
    if (!inReferences.contains(refElement)) {
      inReferences.add(refElement);
    }
  }
@Override
  public synchronized void addInReference(RefElement refElement)