SICP 2.17

;;; Assuming at least 1 element in items
(define (last-pair items)
  (if (null? (cdr items))
      (car items)
      (last-pair (cdr items))))

;;; Assuming at least 1 element in items
(define (last-pair-iter items)
  (define (iter i result)
    (if (null? i)
        result
        (iter (cdr i) (car i))))
  (iter items (car items)))