anchor.diff:  (defmethod next ((iter iterator))
     (with-slots (index end increment id quiet cyclic initial-element
                        accessor bound-check initial-contents) iter
  -    (if (or (funcall bound-check index end) (eq end -1))
  +    (if (or (funcall bound-check index end) (eq end *limit*))
           (let ((current
                  (funcall id (cond
                                ((not (null initial-contents))
  
positive.code:      while (and i j)
       collect (cons i j)))
  
  (defmacro make-iterator (&key (start 0) (end -1) (inc 1) (id #'identity) (cyclic nil)
                             (initial-contents ()) (from-end nil) (initial-element nil))
    (let ((iter (gensym "iterator")))
      `(let ((,iter (make-instance 'iterator :start (or ,start 0)
                                   :end (or (when (not (null ,initial-contents))
                                              (let ((len (length ,initial-contents)))
                                                (if (= ,end -1)
                                                    len
                                                    (when (>= ,end len)
                                                      (error "length out of bounds")))))
                                            ,end)
                                   :inc ,inc :id ,id :cyclic ,cyclic
                                   :initial-contents ,initial-contents
                                   :initial-element ,initial-element)))
  
negative.code:              (progn
                 (rotatef start end)
                 (setf index start
                       bound-check #'>=
                       increment (* -1 ,inc)))
               (setf index start)))
         (to-string ,iter)
         ,iter)))
  
  (defmacro with-iterator ((name &key (start 0) (end *limit*) (increment 1)
                                 (initial-contents nil) (id #'identity)) &body body)
    `(let ((,name (make-iterator :start ,start :end ,end
                                 :inc ,increment :id ,id
  