anchor.diff:  (defun copy-node (node)
     (copy-array node))
   
  +(defun node-size (node)
  +  (fill-pointer node))
  +
   (defun node-get (node index)
     (declare (fixnum index))
     (aref node index))
  
positive.code:           (node-update node next-index
                      (node-push-deep child item length (1- height)))
            (node-push node (node-grow item (1- height)))))))
  
negative.code:     (if (< length 32)
          0
          (ash (rsh (1- length) 5) 5))))
  
  ;; Helper functions related to nodes of the tree
  
  (defun get-node (vector index)
    "Returns node that holds item of given index"
  