private IntSet addAllSubclasses(final int root, final IntSet acc) {
    if (acc.add(root)) {
      final IntSet directSubclasses = myClassToSubclasses.get(root);
      if (directSubclasses != null) {
        directSubclasses.forEach(s -> {
          addAllSubclasses(s, acc);
        });
      }
    }
    return acc;
  }
private IntSet addAllSubclasses(final int root, final IntSet acc)