#![allow(unused_variables)]
#![feature(btree_cursors)]
fn main() {
    use std::collections::BTreeMap;
    use std::ops::Bound;
    let mut map = BTreeMap::from([(1, "a"), (2, "b"), (3, "c"), (4, "d")]);
    let mut cursor = map.lower_bound_mut(Bound::Included(&2));
    assert_eq!(cursor.peek_prev(), Some((& 1, & mut "a")));
    assert_eq!(cursor.peek_next(), Some((& 2, & mut "b")));
    let mut cursor = map.lower_bound_mut(Bound::Excluded(&2));
    assert_eq!(cursor.peek_prev(), Some((& 2, & mut "b")));
    assert_eq!(cursor.peek_next(), Some((& 3, & mut "c")));
    let mut cursor = map.lower_bound_mut(Bound::Unbounded);
    assert_eq!(cursor.peek_prev(), None);
    assert_eq!(cursor.peek_next(), Some((& 1, & mut "a")));
}