public static List<String> toTagList(List<State> states) {
      List<String> tags = new ArrayList<String>();
      if (states.size() > 0) {
        tags.add(states.get(0).getPreviousPreviousTag());
        for (State state : states) {
          tags.add(state.getPreviousTag());
        }
      }
      return tags;
    }