pub struct i32;
pub struct i64;
pub struct isize;
pub struct u32;
pub struct u64;
pub struct usize;

trait Num;

fn (a: N) + (b: N) -> N where N: Num {
  N::add(a, b)
}

fn (a: N) - (b: N) -> N where N: Num {
  N::sub(a, b)
}

fn (a: N) / (b: N) -> N where N: Num {
  N::div(a, b)
}

fn (a: N) * (b: N) -> N where N: Num {
  N::mul(a, b)
}

// precedence a + b < a * b;

pub fn fac(n: I) -> I where I: int {
  if n == 0 {
    return 1
  } else {
    return fac(n-1)
  }
}