Function fib

code/mathematics/intx.test.cpp:7–16

}

intx fib(int n) {
  intx a(0), b(1);
  for (int i = 0; i < n; i++) {
    intx c = a + b;
    a = b;
    b = c;
  }

  return a;
}

intx fac(int n) {
  intx res(1);