anchor.diff:                                                  frame-start frame-end)))
   
         ;; push mesh include files
  -      (map-tree-set nil #'include
  -                    (fold-scene-graph-frames
  -                     (lambda (set frame)
  -                       (fold (lambda (set visual)
  -                               (let ((g (scene-visual-geometry visual)))
  -                                 (if (scene-mesh-p g)
  -                                     (tree-set-insert set
  -                                                      (scene-mesh-inc (scene-mesh-file g)))
  -                                     set)))
  -                             set
  -                             (ensure-list (scene-frame-visual frame))))
  -                     (make-tree-set #'string-compare)
  -                     scene-graph))
  +      (let ((mesh-set (make-tree-set #'string-compare)))
  +        (do-scene-graph-visuals ((frame-name visual) scene-graph)
  +          (declare (ignore frame-name))
  +          (let ((geom (scene-visual-geometry visual)))
  +            (when (scene-mesh-p geom)
  +              (tree-set-insertf mesh-set
  +                                (scene-mesh-inc (scene-mesh-file geom))))))
  +        (map-tree-set nil #'include mesh-set))
         (map nil #'include (reverse (ensure-list include)))
         ;; version
         (thing (pov-version 3.7)))
  
positive.code:                           (scene-graph-frame-map ,scene-graph))
              ,result)))
  
    ;; `(progn
    ;;    (loop for ,frame-variable being the hash-values of (scene-graph-frame-map ,scene-graph)
    ;;       do (progn ,@body))
    ;;    ,result))
  
  (defun fold-scene-graph-frames (function initial-value scene-graph)
    (fold-tree-map (lambda (accum key value)
  
negative.code:                  initial-value
                   (scene-graph-frame-map scene-graph)))
  
  
  (defun scene-graph-lookup (scene-graph frame-name)
    (tree-map-find (scene-graph-frame-map scene-graph)
                   frame-name))
  
  
  ;; Find the relative transform of the scene frame
  (defgeneric scene-frame-tf (object))
  