(with_import "./rb.kp"
(let (
    first empty
    _ (println first " contains? " 1 " ? " (contains? first 1))
    second (insert first 1)
    _ (println second " contains? " 1 " ? " (contains? second 1))
    third (insert second 2)
    _ (println third " contains? " 1 " ? " (contains? third 1))
    _ (println third " contains? " 2 " ? " (contains? third 2))
    fourth (insert third 3)
    _ (println fourth " contains? " 1 " ? " (contains? fourth 1))
    _ (println fourth " contains? " 2 " ? " (contains? fourth 2))
    _ (println fourth " contains? " 3 " ? " (contains? fourth 3))
    _ (println fourth " contains? " 4 " ? " (contains? fourth 4))
) nil))