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:              (setf (lambda-information-body lambda)
                     `((let ((,new-env (sys.int::make-simple-vector ',(1+ (length local-env)))))
                         ,@(when (rest *environment-chain*)
                             (list (list (sys.int::function-symbol '(setf sys.int::%svref))
                                         (second (second *environment-chain*))
                                         new-env
                                         ''0)))
                         ,@(mapcar (lambda (arg)
                                     (list (sys.int::function-symbol '(setf sys.int::%svref))
                                           arg
                                           new-env
                                           `',(1+ (position arg local-env))))
                                   (remove-if #'localp (lambda-information-required-args lambda)))
                         ,@(mapcar (lambda (arg)
                                     (list (sys.int::function-symbol '(setf sys.int::%svref))
                                           (first arg)
                                           new-env
                                           `',(1+ (position (first arg) local-env))))
                                   (remove-if #'localp (lambda-information-optional-args lambda)
                                              :key #'first))
                         ,@(mapcar (lambda (arg)
                                     (list (sys.int::function-symbol '(setf sys.int::%svref))
                                           (third arg)
                                           new-env
                                           `',(1+ (position (third arg) local-env))))
  