anchor.diff:  depth-first walk."
     (with-loc loc
       (when (and loc loc-path)
  -      (cond ((node-right loc-path) (replace-by-right loc-path))
  -            ((node-left loc-path) (replace-by-left loc-path))))))
  +      (cond ((loc-right loc-path) (replace-by-right loc-path))
  +            ((loc-left loc-path) (replace-by-left loc-path))))))
   
   (defun replace-by-right (loc-path)
     "Replaces the current node at loc by the node at the right."
     (when loc-path
  -    (let ((right (node-right loc-path)))
  +    (let ((right (loc-right loc-path)))
         (list (car right)
  -            (make-node :left (node-left loc-path)
  -                       :ppath (node-ppath loc-path)
  -                       :right (cdr right))))))
  +            (make-loc :left (loc-left loc-path)
  +                      :ppath (loc-ppath loc-path)
  +                      :right (cdr right))))))
   
   (defun replace-by-left (loc-path)
     "Replaces the current node at loc by the node at the left."
     (when loc-path
  -    (let ((left (node-left loc-path)))
  +    (let ((left (loc-left loc-path)))
         (list (car left)
  -            (make-node :left (cdr left)
  -                       :ppath (node-ppath loc-path)
  -                       :right (node-right loc-path))))))+            (make-loc :left (cdr left)
  +                      :ppath (loc-ppath loc-path)
  +                      :right (loc-right loc-path))))))
  
positive.code: the top."
    (with-loc loc
      (when loc-path
        (list (concatenate 'list (reverse (node-left loc-path))
                           (when loc-tree
                             (cons loc-tree (node-right loc-path))))
              (node-ppath loc-path)))))
  
  (defun go-next (loc)
    "Moves to the next loc in the hierarchy, depth-first. When reaching the end,
  
negative.code:   (with-loc loc
      (when loc-path
        (list loc-tree
              (make-loc :left (loc-left loc-path)
                        :ppath (loc-ppath loc-path)
                        :right (cons tree (loc-right loc-path)))))))
  
  (defun insert-left (loc tree)
    "Inserts the item as the left sibling of the node at this loc, without
  