(define fact 
  (lambda (n) 
    (if (= n 0) 
        1  ;then part
        (* n (fact (- n 1))) ; else part
        )
    )
  )

(fact 10)
(fact 11)
(fact 12)
(fact 13)
(fact 14)
(fact 15)
(fact 100)
(fact 1000)
(fact 10000)