anchor.diff:  (defmethod sheet-disown-child ((sheet sheet-multiple-child-mixin)
   			       (child sheet-parent-mixin)
   			       &key (errorp t))
  -  (declare (ignorable errorp))
  +  (declare (ignore errorp))
     (setf (sheet-children sheet) (delete child (sheet-children sheet))))
  -
  -(defmethod sheet-disown-child :after ((sheet sheet-multiple-child-mixin)
  -				     (child sheet-parent-mixin)
  -				     &key (errorp t))
  -  (declare (ignorable sheet errorp))
  -  (note-sheet-disowned child))
   
   (defmethod raise-sheet-internal (sheet (parent sheet-multiple-child-mixin))
     (setf (sheet-children parent)
  
positive.code: (defmethod sheet-disown-child :after (sheet
  				      (child sheet-parent-mixin)
  				      &key (errorp t))
    (declare (ignore sheet errorp))
    (setf (sheet-parent child) nil))
  
  (defmethod sheet-siblings ((sheet sheet-parent-mixin))
    (when (not (sheet-parent sheet))
  
negative.code:     (note-sheet-grafted sheet)))
  
  (defmethod note-sheet-disowned ((sheet sheet))
    nil)
  
  (defmethod note-sheet-region-changed ((sheet sheet))
    nil) ;have to change
  