anchor.diff:    (declare (type array m)
              (values (simple-array * (*))))
     (let ((dims (array-dimensions m)))
  -    (labels ((frob (m dims &optional upper-offsets)
  +    (labels ((frob (m dims &optional (upper-offset 1))
                  (let ((this-dim (car dims))
                        (rest-dim (cdr dims)))
                    (cond 
  
positive.code:                         (setf (aref retv n)
                                (row-major-aref 
                                 m  
                                 (apply #'array-row-major-index
                                        m 
                                        ;; FIXME: much consing
                                        (append upper-offsets
                                                (list n))))))))))))
        (frob m dims))))
  
  ;; (compute-array-vector* #2A((1 2 3 4) (4 3 2 1)))
  
negative.code:                       (dotimes (n this-dim retv)
                          (setf (aref retv n)
                                (frob m rest-dim 
                                      (* upper-offset n))))))
                     (t 
                      (let ((retv
                             (make-array this-dim
  