anchor.diff:    }
   
     /**
  -   * Returns a new [BitList] with all the bits of the receiver inverted.
  +   * Returns the complement of the receiver.
  +   *
  +   * The new [BitList] has all the bits of the receiver inverted.
      */
     BitList operator ~ () {
       var result = new BitList(_length);
  
positive.code:   }
  
    /**
     * Returns a new [BitList] with all the bits set that are set in the
     * receiver and in [other]. The receiver and [other] need to have
     * the same length, otherwise an exception is thrown.
     */
    BitList operator & (BitList other) {
      assert(_length == other._length);
  
negative.code:   }
  
    /**
     * Returns the union of the receiver and [other].
     *
     * The new [BitList] has all the bits set that are either set in the
     * receiver or in [other]. The receiver and [other] need to have the
     * same length, otherwise an exception is thrown.
     */
    BitList operator | (BitList other) {
      assert(_length == other._length);
  