anchor.diff:             (setf (node-right h) (insert-node (node-right h) key value tree lessp)))
             (t
              (setf (node-value h) value)))
  +        
           (when (node-red-p (node-right h))
             (setf h (lean-left h)))
           h)))
  
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: 
      AGPL3
      
      Copyright Pascal J. Bourguignon 2009 - 2015
      
      This program is free software: you can redistribute it and/or modify
      it under the terms of the GNU Affero General Public License as published by
  