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