fn twice<T: Copy + std::ops::Add<Output = T>>(x: T) -> T { x + x }
fn span<T: PartialOrd + std::ops::Sub<Output = T>>(a: T, b: T) -> T {
    if a > b { a - b } else { b - a }
}

fn main() { assert_eq!(twice(3_i64),6);assert_eq!(twice(1.25_f64),2.5);assert_eq!(span(9_i64,2),7);assert_eq!(span(2_i64,9),7);assert_eq!(span(3.0_f64,1.5),1.5); }