anchor.diff:   */
   abstract class FixedLengthListBase<E> extends ListBase<E> {
     void operator[]=(int index, E value);
  -
  -  List<E> get reversed => new ReversedListView<E>(this, 0, null);
   
     void sort([Comparator<E> compare]) {
       Sort.sort(this, compare);
  
positive.code: 
    bool moveNext() {
      if (_list.length != _originalLength) {
        throw new ConcurrentModificationError(list);
      }
      if (_index <= _start) return false;
      _index -= 1;
  
negative.code:   }
  
    String toString() => ToString.collectionToString(this);
  
    List<E> get reversed {
      return new ReversedListView(this, 0, null);
    }
  }
  
  /**
  