anchor.diff:  					   (if list
   					       (setf ,tail (last list)))
   					   nil))
  +	   (declare (ignorable
  +		     ,@(loop for collector in collectors
  +			     collect `#',collector
  +			     collect `#',(intern (format nil "N~A" collector)))))
   	   ,@body)
   	 (values ,@collectors)))))
   
  
positive.code: 						       (setf ,tail (list thing)))
  						 (setf ,collector
  						       (setf ,tail (list thing))))
  					     THING)
  			collect `(,(intern (format nil "N~A" collector))
  					   (list)
  					   (if ,collector
  
negative.code: 		  (if list
  		      (setf ,tail (last list)))
  		  nil))
  	 (declare (ignorable #'collect #'ncollect))
  	 ,@body)
         ,collector)))
  
  