(define (avl-tree-maintain-balance tree stack origin child l-subtree-mod
                                   r-subtree-mod called-on)
  (let* loop ((parent origin) (child child)
	      (avl-n-m-bal (lambda () (avl-node-mod-balance
				       parent (if (eq? (avl-node-l-subtree parent) child)
						  l-subtree-mod
						  r-subtree-mod))
				   (loop (avl-stack-pop! stack) parent))))
	(if (null? parent)
	    0
	    (case (avl-node-balance child)
	      ((0 4) 1)
	      ((1 3) (if (eq? called-on 'deletion)
			 2)
	       (avl-n-m-bal))
	      (else (if (eq? called-on 'insertion)
			3)
		    (avl-n-m-bal))))))