structure X = struct
fun main n = let
fun a (x, 0) = d x
| a (x, n) = b (x, n - 1)
and b (x, n) = c (x, n)
and c (x, n) = a (x, n)
and d x = e (x, 3)
and e (x, 0) = f x
| e (x, n) = e (x, n - 1)
and f 0 = SMLofNJ.Internals.BTrace.trigger ()
| f n = n * g (n - 1)
and g n = a (n, 3)
in
f n
end
end