anchor.diff:  
   (in-package :sys.int)
   
  -;;; FIXME: Should be a class.
  +;;; FIXME: Should be a class, but this is much faster.
  +;;; ### Specialize in TYPEP?
   (deftype sequence ()
     '(or vector list))
   
  
positive.code:                       (dotimes (i n)
                          (setf (elt sequence-1 (+ start1 i)) (elt sequence-2 (+ start2 i)))))))))))
    sequence-1)
  
  (defmacro object-type-dispatch (object &body body)
    "Fast CASE on (%OBJECT-TAG object)"
  
negative.code:     (error "TEST and TEST-NOT specified")))
  
  (defun length (sequence)
    (cond ((null sequence) 0)
          ((consp sequence)
           (or (list-length sequence)
               (error 'simple-type-error
                      :expected-type 'sequence
                      :datum sequence
                      :format-control "List ~S is circular."
                      :format-arguments (list sequence))))
          ((%simple-1d-array-p sequence)
           (%object-header-data sequence))
          ((and (complex-array-p sequence)
                (eql (%object-header-data sequence) 1)) ; rank 1
           (let ((fill-pointer (%object-ref-t sequence +complex-array-fill-pointer+)))
             (or fill-pointer
                 (%object-ref-t sequence +complex-array-axis-0+))))
          (t
           (error 'type-error
                  :expected-type 'sequence
                  :datum sequence))))
  
  (defun elt (sequence index)
    (check-type sequence sequence)
  