set.add(tooHigh);
      set.add(tooLow);
      return checkedCreate(set).subSet(tooLow + 1, tooHigh);
    }
  }

  @GwtIncompatible // NavigableSet
  public static class ContiguousSetDescendingGenerator extends AbstractContiguousSetGenerator {
    @Override
    protected SortedSet<Integer> create(Integer[] elements) {
      return checkedCreate(nullCheckedTreeSet(elements)).descendingSet();
    }