anchor.diff:     (make-pathname :name (filename plot)
                     :type "data"
                     :directory (filepath plot))))
  -
  -;;; ---------------------------------------------------------------------------
   
   (defclass* gnuplot (plot-abstract)
     ((filename "plot" ia)
  
positive.code:       (format out "set yrange [~:[*~;~:*~A~]:~:[*~;~:*~A~]] ~C" 
                (item-at settings :ymin) (item-at settings :ymax) #\Linefeed))))
  
  ;;; ---------------------------------------------------------------------------
  
  (defmethod write-plot-settings ((plot plot-data-set) out)
    (let ((first? t)
          (settings (settings plot)))
  
negative.code:   
    (values plot))
  
  (defmethod make-data-set (plot-kind data
                            &rest args
                            &key (comment nil)
  