#![allow(unused_variables)]
fn main() {
    use std::collections::BTreeSet;
    let mut a = BTreeSet::new();
    a.insert(1);
    a.insert(2);
    a.insert(3);
    let mut b = BTreeSet::new();
    b.insert(3);
    b.insert(4);
    b.insert(5);
    a.append(&mut b);
    assert_eq!(a.len(), 5);
    assert_eq!(b.len(), 0);
    assert!(a.contains(& 1));
    assert!(a.contains(& 2));
    assert!(a.contains(& 3));
    assert!(a.contains(& 4));
    assert!(a.contains(& 5));
}