#fload "tlib.sf"

; fixnum tak

(define (tak x y z)
  (if (< y x)
      (tak (tak (- x 1) y z)
           (tak (- y 1) z x)
           (tak (- z 1) x y))
       z))


; list tak

(define (listn n)
  (if (= 0 n)
      '()
      (cons n (listn (- n 1)))) )

(define (length l) 
  (define (length-aux l n) 
    (if (pair? l) 
        (length-aux (cdr l) (+ n 1)) 
        n))
  (length-aux l 0))

(define (shorterp x y)
  (and (pair? y)
       (or (null? x)
           (shorterp (cdr x) (cdr y)))))

(define l18 (listn 18))
(define l12 (listn 12))
(define  l6 (listn 6))

(define (ltak x y z)
  (if (not (shorterp y x))
      z
      (ltak (ltak (cdr x) y z)
            (ltak (cdr y) z x)
            (ltak (cdr z) x y))))