#![allow(unused_variables)]
fn main() {
    use std::collections::BTreeMap;
    let mut map = BTreeMap::new();
    map.insert(1, "a");
    map.insert(2, "b");
    while let Some((key, _val)) = map.pop_last() {
        assert!(map.iter().all(| (k, _v) | * k < key));
    }
    assert!(map.is_empty());
}