anchor.diff:  (defun draw-options-default (&key
                                  (options *draw-options*)
                                  (no-shadow (draw-option options :no-shadow))
  +                               (specular (draw-option options :specular))
                                  (color (draw-option options :color))
                                  (alpha (draw-option options :alpha))
                                  (visual (draw-option options :visual))
  
positive.code:                                (collision (draw-option options :collision)))
    (list* (cons :no-shadow no-shadow)
           (cons :color color)
           (cons :alpha alpha)
           (cons :visual visual)
           (cons :collision collision)
  
negative.code: (defparameter *draw-options*
    '((:no-shadow . nil)
      (:color . (0 0 0))
      (:specular . (0 0 0))
      (:alpha . 1d0)
      (:visual . t)
      (:collision . t)
  