> (trace fac)
(fac)
> (trace apply-cont)
(apply-cont)
> (fac 5 (halt-cont))
|(fac 5 (halt-cont))
|(fac 4 (multiplication-cont 5 (halt-cont)))
|(fac 3 (multiplication-cont 4 (multiplication-cont 5 (halt-cont))))
|(fac 2
      (multiplication-cont
       3
       (multiplication-cont 4 (multiplication-cont 5 (halt-cont)))))
|(fac 1
      (multiplication-cont
        2
        (multiplication-cont
          3
          (multiplication-cont 4 (multiplication-cont 5 (halt-cont))))))
|(fac 0
      (multiplication-cont
       1
       (multiplication-cont
	2
	(multiplication-cont
	 3
	 (multiplication-cont 4 (multiplication-cont 5 (halt-cont)))))))
|(apply-cont
   (multiplication-cont
     1
     (multiplication-cont
       2
       (multiplication-cont
         3
         (multiplication-cont 4 (multiplication-cont 5 (halt-cont))))))
   1)
|(apply-cont
  (multiplication-cont
   2
   (multiplication-cont
    3
    (multiplication-cont 4 (multiplication-cont 5 (halt-cont)))))
  1)
|(apply-cont
   (multiplication-cont
     3
     (multiplication-cont 4 (multiplication-cont 5 (halt-cont))))
   2)
|(apply-cont (multiplication-cont 4 (multiplication-cont 5 (halt-cont))) 6)
|(apply-cont (multiplication-cont 5 (halt-cont)) 24)
|(apply-cont (halt-cont) 120)
|120
120