anchor.diff:    }
   
     /**
  -   * insert an element after this.
  +   * Insert an element after this element in this element's linked list.
  +   *
  +   * This entry must be in a linked list when this method is called.
  +   * The [entry] must not be in a linked list.
      */
     void insertAfter(E entry) {
       _list._insertAfter(this, entry);
     }
   
     /**
  -   * Insert an element before this.
  +   * Insert an element before this element in this element's linked list.
  +   *
  +   * This entry must be in a linked list when this method is called.
  +   * The [entry] must not be in a linked list.
      */
     void insertBefore(E entry) {
       _list._insertAfter(_previous, entry);
  
positive.code: 
  
  /**
   * Entry element for a [LinkedList]. Any entry must extend this class.
   */
  abstract class LinkedListEntry<E extends LinkedListEntry<E>>
      implements _LinkedListLink {
  
negative.code:   }
  
    /**
     * Add [entry] to the beginning of the linked list.
     */
    void addFirst(E entry) {
      _insertAfter(this, entry);
    }
  
    /**
     * Add [entry] to the end of the linked list.
     */
    void add(E entry) {
      _insertAfter(_previous, entry);
    }
  
    /**
     * Add [entries] to the end of the linked list.
     */
    void addAll(Iterable<E> entries) {
      entries.forEach((entry) => _insertAfter(_previous, entry));
    }
  
    /**
     * Remove [entry] from the linked list.
     *
     * Returns false and does nothing if [entry] is not in this linked list.
     *
     * This is equivalent to calling `entry.unlink()` if the entry is in this
     * list.
     */
    bool remove(E entry) {
      if (entry._list != this) return false;
  