anchor.diff:            (pov-integer-vector-y object)
             (pov-integer-vector-z object)))
   
  +(defmethod object-rope ((object pov-integer-vector))
  +  (rope '|<|
  +        (int-string (pov-integer-vector-x object)) '|, |
  +        (int-string (pov-integer-vector-y object)) '|, |
  +        (int-string (pov-integer-vector-z object)) '|>|))
  +
   (defstruct (pov-value (:constructor pov-value (value)))
     value)
   
  
positive.code:           (pov-uv-vector-u object)
            (pov-uv-vector-v object)))
  
  
  (defstruct pov-matrix
    elements)
  
negative.code:   (format stream "~&#include ~S"
            (pov-include-file object)))
  
  (defmethod object-rope ((object pov-include))
    (rope '|#include | (pov-include-file object)))
  
  (defstruct (pov-sequence (:constructor pov-sequence (statements)))
    statements)
  
  (defmethod print-object ((object pov-sequence) stream)
    (loop for x in (pov-sequence-statements object)
       do (print-object x stream)))
  
  (let ((newline (format nil "~%")))
    (defmethod object-rope ((object pov-sequence))
      (fold (lambda (rope object)
              (rope rope newline (object-rope object)))
            ""
            (pov-sequence-statements object))))
  
  (defun pov-quality (float-quality)
    "Return numeric povray quality for proportional to RATIO.
  