anchor.diff:                     (and (<= start2 start1) (< start1 end2))
                      (and (< start2 end1) (<= end1 end2))))
         (when (eql start1 start2)
  -        (return-from replace sequence-1))
  +        (return-from replace-known-args sequence-1))
         (setf copy-backwards t))
       (macrolet ((fast-vector (type)
                    `(if (and (typep sequence-1 '(array ,type (*)))
  
positive.code: 
  (in-package :sys.int)
  
  ;;; FIXME: Should be a class.
  (deftype sequence ()
    '(or vector list))
  
  
negative.code: (defun notevery (predicate first-sequence &rest more-sequences)
    (not (apply 'every predicate first-sequence more-sequences)))
  
  (defun replace-known-args (sequence-1 sequence-2 start1 end1 start2 end2)
    (unless end1 (setf end1 (length sequence-1)))
    (unless end2 (setf end2 (length sequence-2)))
    (assert (<= 0 start1 end1 (length sequence-1)))
  