anchor.diff:  			   (funcall displayer stream x y datum)
   			   ;; Forcing the x buffer is nice here, but it is
   			   ;; extremely expensive.  It slows drawing by 4x.
  -			   #+slow (force-output stream)))
  +			   ;;  (force-output stream)
  +                           ))
   		(data self)))))
   
   (defmethod datum-displayer ((self essential-graph-data-map-mixin) graph)
  
positive.code: 
  (defmethod map-data ((dataset t) function (data sequence))
    "Map FUNCTION over each datum."
    #-(or sbcl cmu)
    (declare (downward-funarg function))
    (map nil function data))
  
  (defmethod map-data-xy ((dataset ESSENTIAL-GRAPH-DATA-MAP-MIXIN) function data)
    "Map function over each x y pair."
    #-(or sbcl cmu)
    (declare (downward-funarg function))
    (declare (compiled-function function))
    (map-data dataset
  	    #'(lambda (datum)
  		(declare (downward-function))
  
negative.code:   ;; hence the consing here.
    (list '("Line" :value :line) '("Line-Symbol" :value :line-symbol)))
  
  (defmethod transformation-offsets ((any t)) (values 0 0))
  
  (defmethod dont-record-output-history ((dataset t))
  