code: private static Clique valueOfHelper(int[] relativeIndices) {
      // if clique already exists, return that one
      Clique c = new Clique();
      c.relativeIndices = relativeIndices;
      return intern(c);
    }
docs: This version assumes relativeIndices array no longer needs to
  be copied. Further it is assumed that it has already been
  checked or assured by construction that relativeIndices
  is sorted.