code: public Set<T> internAll(Set<T> s) {
      Set<T> result = Generics.newHashSet();
      for (T o : s) {
        result.add(intern(o));
      }
      return result;
    }
docs: Returns a <code>Set</code> such that each element in the returned set
  is a unique object e' that .equals the corresponding element e in the
  original set.