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