int -> int fix(<int -> int> -> int -> int f) {
  T -> int -> int g = fun(T x) { f(fun(int y) { x.f x y; }); };
  g (new Y(f = g));
}

struct Y : T {
  init T -> int -> int f;
}

int factorialor(int -> int factorial) (int x) {
  if(x == 0) 1
  else       x * factorial(x - 1);
}

int main(int n) { fix factorialor n; }