#![allow(dead_code, deprecated, unused_variables, unused_mut)]
fn sq_then_to_string(x: u32) -> Option<String> {
    x.checked_mul(x).map(|sq| sq.to_string())
}
fn main() {
    assert_eq!(Some(2).and_then(sq_then_to_string), Some(4.to_string()));
    assert_eq!(Some(1_000_000).and_then(sq_then_to_string), None);
    assert_eq!(None.and_then(sq_then_to_string), None);
}