anchor.diff:     */
     void forEach(void action(E entry)) {
       int modificationCount = _modificationCount;
  -    _LinkedListLink current = _next;
  +    E current = _next;
       while (!identical(current, this)) {
         action(current);
         if (modificationCount != _modificationCount) {
  
positive.code:    * Return the succeeding element in the list.
     */
    E get next {
      if (_next == _list) return null;
      return _next;
    }
  
    /**
     * Return the preceeding element in the list.
     */
    E get previous {
      if (_previous == _list) return null;
      return _previous;
    }
  
    /**
  
negative.code:     _length++;
    }
  
    void _unlink(LinkedListEntry<E> entry) {
      _modificationCount++;
      entry._next._previous = entry._previous;
      entry._previous._next = entry._next;
  