#![allow(unused_variables)]
fn main() {
    use std::collections::BTreeSet;
    let sup = BTreeSet::from([1, 2, 3]);
    let mut set = BTreeSet::new();
    assert_eq!(set.is_subset(& sup), true);
    set.insert(2);
    assert_eq!(set.is_subset(& sup), true);
    set.insert(4);
    assert_eq!(set.is_subset(& sup), false);
}