anchor.diff:    (error "I don't understand RECOMPUTE-EXTENT-FOR-CHANGED-CHILD - mikemac"))
   
   (defmethod tree-recompute-extent ((record output-record))
  -  (with-slots (parent children x-min y-min x-max y-max) record
  +  (with-slots (parent children x1 y1 x2 y2) record
       (if (null children)
  -	(setq x-min 0
  -	      y-min 0
  -	      x-max 0
  -	      y-max 0)
  +	(setq x1 0
  +	      y1 0
  +	      x2 0
  +	      y2 0)
         (with-bounding-rectangle* (left top right bottom) (first children)
   	(loop for child in (rest children)
   	      do (with-bounding-rectangle* (l1 t1 r1 b1) child
  
positive.code:     (setq children (delete child children))))
  
  (defmethod clear-output-record ((record output-record))
    (with-slots (children x-min y-min x-max y-max) record
      (setq children nil
  	  x-min 0
  	  y-min 0
  	  x-max 0
  	  y-max 0)))
  
  (defmethod output-record-count ((record output-record))
    (length (output-record-children record)))
  
negative.code: 			 top (min top t1 b1)
  			 right (max right l1 r1)
  			 bottom (max bottom t1 b1))))
  	(setq x1 left
  	      y1 top
  	      x2 right
  	      y2 bottom)))
      (if parent
  	(recompute-extent-for-changed-child parent record x1 y1 x2 y2))))
  
  (defclass standard-sequence-output-record (displayed-output-record)
    (
  