transient sclass DoubleWordIndex<A> {
  new WordIndex<A> index1; // forwards (normal words)
  new WordIndex<A> index2; // backwards (reversed words)
  
  *() {}
  
  *(Comparator<A> valueComparator) {
    index1 = new WordIndex(valueComparator);
    index2 = new WordIndex(valueComparator);
  }
  
  *(Map<A, S> map) { fOr (A a, S text : map) add(a, text); }
  
  void add(A a, S text) {
    index1.add(a, text);
    index2.add(a, text);
  }
  
  Set<A> get(S word) {
    ret index1.get(word);
  }
  
  L<IntRange> wordRanges(S text) {
    ret index1.wordRanges(text);
  }
}