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