(define (same-struct l1 l2)
  (cond ((and (atom? l1)
              (atom? l2)) #t)
        ((and (pair? l1)
              (pair? l2)) (and (same-struct (car l1)
                                            (car l2))
                               (same-struct (cdr l1)
                                            (cdr l2))))
        (else #f)))