code: private static <K extends Comparable<? super K>, V> Collection<@KeyFor("#1") K> sortedKeySet(
        Map<K, V> m) {
      ArrayList<@KeyFor("#1") K> theKeys = new ArrayList<>(m.keySet());
      Collections.sort(theKeys);
      return theKeys;
    }
docs: Returns a sorted version of m.keySet().
  
  @param <K> type of the map keys
  @param <V> type of the map values
  @param m a map whose keyset will be sorted
  @return a sorted version of m.keySet()