anchor.diff:  #+(or)
   (merge-arguments '(:a (1) :b (2)) '(:c (3) :a (2))) 
   
  +#+(or)
   (defun _render-one (doc)
     (let ((*current-document* doc)
   	(*render-active-functions*
  
positive.code:   (transfer-selected-properties 
     parent child 
     (set-difference (collect-keys (properties child))
  		   (list :footnote :style-sheet :style-sheets :title))))
  
  (defun transfer-selected-properties (parent child properties)
    (let ((*current-document* parent))
  
negative.code: 				  ,@*render-active-functions*)
  				*render-active-functions*)))))
  	   (render-to-stream doc format destination)))
      (setf (children main-document) (mapcar #'first docs))
      (values main-document docs)))
  
  (defun merge-arguments (args-1 args-2)
  