anchor.diff:  
   (defvar *command-stream* nil
     "The default stream to which commands and inline data are written by
  -WRITE-COMMAND.")
  +  WRITE-COMMAND.")
   
   (defmacro with-command-stream ((stream) &body body)
     "Binds *COMMAND-STREAM* to STREAM routing all command output to
  -STREAM by default."
  +  STREAM by default."
     `(let ((*command-stream* ,stream))
        ,@body))
   
  
positive.code: 
  (defgeneric write-command (command stream)
    (:documentation "Write the gnuplot COMMAND to STREAM. Commands
  represented by the classes PLOT, SET-COMMAND, etc."))
  
  (defgeneric write-mapping (mapping stream)
    (:documentation "Write the gnuplot MAPPING to STREAM."))
  
negative.code: (defclass command ()
    ()
    (:documentation "A gnuplot command. There are separate classes for
    plot/splot, etc."))
  
  (defclass plot ()
    ((kind :type (member :2d :3d) :initform :2d :initarg :kind :reader kind)
  