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

struct Y(T -> int -> int f) : T { }

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

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