anchor.diff:                                              :key #'third))
                          ,@(when (and (lambda-information-rest-arg lambda)
                                       (not (localp (lambda-information-rest-arg lambda))))
  -                               (list (list (sys.int::function-symbol '(setf %svref))
  +                               (list (list (sys.int::function-symbol '(setf sys.int::%svref))
                                              (lambda-information-rest-arg lambda)
                                              new-env
                                              `',(1+ (position (lambda-information-rest-arg lambda) local-env)))))
  
positive.code:                   (env-offset (1+ (position (second form) (gethash (first *environment*) *environment-layout*)))))
                (setf (block-information-env-var (second form)) env-var
                      (block-information-env-offset (second form)) env-offset)
                (list (list (sys.int::function-symbol '(setf %svref))
                            (second form)
                            env-var
                            `',env-offset))))
  
negative.code:                                                          *environment-chain*))
                               (*environment* (list* form *environment*)))
                           (if (rest *environment-chain*)
                               (list* (list (sys.int::function-symbol '(setf sys.int::%svref))
                                            (second (second *environment-chain*))
                                            new-env
                                            ''0)
  