anchor.diff:    (format t "~A~A~A+---- NIL~A~%" indentation bar *black* *normal*))
   
   (defmethod dump ((self node) &optional (indentation "") (bar " "))
  +  (dump (node-left  self) (concat indentation bar "    ") "|")
  +  (format t "~A~A    |~%" indentation bar)
     (format t "~A~A~A+---- ~A: ~A~A~%" indentation bar
             (if (node-red-p self) *red* *black*) 
             (node-key self) (node-value self)
             *normal*)
     (format t "~A~A    |~%" indentation bar)
  -  (dump (node-left  self) (concat indentation bar "    ") "|")
  -  (format t "~A~A    |~%" indentation bar)
  -  (dump (node-right self) (concat indentation bar "    ") " "))
  +  (dump (node-right self) (concat indentation bar "    ") "|"))
   
   
   (defmethod dump ((self tree) &optional (indentation "") (bar " "))
  
positive.code:                  split-four-node move-red-left move-red-right))
  
  (defun rotate-left (h)
    (let ((x (node-right h)))
      (setf (node-right h) (node-left x)
            (node-left x) h)
      x))
  
  
  (defun rotate-right (h)
    (let ((x (node-left h)))
      (setf (node-left h) (node-right x)
            (node-right x) h)
      x))
  
  
  (defun lean-left (h)
    "Samre as rotate-left, plus update colors."
    (let ((x (node-right h)))
      (setf (node-right h) (node-left x)
            (node-left x) h
            (node-color x) (node-color h)
            (node-color h) :red)
      x))
  
  
  
negative.code:         (incf (tree-count tree))
          (make-node :key key :value value :color :red))
        (progn
          
          (when (and (node-red-p (node-left h))
                     (node-red-p (node-left (node-left h))))
            (setf h (split-four-node h)))
  
          (cond
            ((funcall lessp key (node-key h))
             (setf (node-left  h) (insert-node (node-left  h) key value tree lessp)))
  