fn do_stuff<'a>(mut x: &'a i32, y: &'a i32) {
    println!("{} {}", x, y);
    x = y;
    println!("{} {}", x, y);
}

fn main() {
   let a = 5;
   let b = 6;

   let s = &a;
   let t = &b;

   println!("{} {} {} {}", a, b, s, t);

   do_stuff(s, t);

   println!("{} {} {} {}", a, b, a, t);
}