(define factorial    ; 1 x 2 x ... x n
       (lambda (n)
         (if (= n 1)
             1
             (* (factorial (- n 1)) n))))
     
     (define sum-of-first ; 1 + 2 + ... + n
       (lambda (n)
         (if (= n 1)
             1
             (+ (sum-of-first (- n 1)) n))))