anchor.diff:    (declare (type hash-table tf-absolute-map))
     (labels ((rec (frame-name)
                (cond
  -               ((null frame-name) ; global frame
  +               ((frame-name-global-p frame-name) ; global frame
                   (tf nil))
                  ((gethash frame-name tf-absolute-map) ; already in hash
                   (gethash frame-name tf-absolute-map))
  
positive.code: (defun frame-name-compare (a b)
    (rope-compare-lexographic a b))
  
  (defstruct frame-inertial
    (mass 0d0 :type double-float)
    (inertia nil))
  
negative.code:       (make-mesh-data :vertex-vectors (vec-flatten verts)
                        :vertex-indices (fnvec-flatten indices)))))
  
  
  
  (defun scene-graph-dot (scene-graph &key output)
    (output-dot output
                (lambda (s)
                  (labels ((sanitize (name)
                             (substitute #\_ #\- name))
                           (node (frame)
                             (let ((n (scene-frame-name frame))
                                   (shape (if (scene-frame-joint-p frame)
                                              "oval"
                                              "box")))
  
                               (format s "~&  ~A[label=\"~A\",shape=~A];"
                                       (sanitize n)
                                       n
                                       shape)))
                           (edge (frame)
                             (let ((n (scene-frame-name frame))
                                   (p (scene-frame-parent frame))
                                   (q (if (scene-frame-joint-p frame)
                                          (scene-frame-joint-configuration-name frame)
                                          "")))
                             (format s "~&  ~A -> ~A[label=\"~A\"];"
                                     (if (frame-name-global-p p)
                                         "ROOT"
                                         (sanitize p))
                                     (sanitize n)
                                     (sanitize q)))))
                    (format s "~&digraph {  ~&")
                    (do-scene-graph-frames (frame scene-graph)
                      (node frame))
                    (do-scene-graph-frames (frame scene-graph)
                      (edge frame))
                    (format s "~&}~&")))))
  
  (defun scene-graph-pov-frame (scene-graph
                                &key
                                  render
  