anchor.diff:  			  (left node))))
   
   (defmethod delete-child ((node 3-node) child)
  -  (let ((2-node-class (2-node-class (tree node))))
  +  (let ((2-node-class (2-node-class (tree node)))
  +	(parent (parent node)))
       (if (eq child (left node))
   	(replace (parent node)
   		 node
   		 (make-instance 2-node-class
  +		   :parent parent
   		   :left (middle node)
   		   :right (right node)))
   	(if (eq child (middle node))
   	    (replace (parent node)
   		     node
   		     (make-instance 2-node-class
  +		       :parent parent
   		       :left (left node)
   		       :right (right node)))
   	    (replace (parent node)
   		     node
   		     (make-instance 2-node-class
  +		       :parent parent
   		       :left (left node)
   		       :right (middle node)))))))
   
  
positive.code: (defmethod replace-and-shrink ((node 3-node) old-child new-child)
    (let ((2-node-class (2-node-class (tree node)))
  	(3-node-class (3-node-class (tree node)))
  	(left (left node))
  	(middle (middle node))
  	(right (right node)))
  
negative.code: 	       (replace (parent node)
  			node
  			(make-instance 2-node-class
  			  :parent parent
  			  :left (make-instance 3-node-class
  				  :left (left left)
  				  :middle (right left)
  