refinement<K, V >

    Key is K

    Value is V 

    Map[Key, Value] is HashtableChain<K, V> {
        make: --> Map[Key, Value] is HashtableChain();
        put: Map[Key, Value] k:Key v:Value --> Map[Key, Value] is void put(K k, V v);
        get: Map[Key, Value] k:Key -->? Value is V get(K k);
        remove: Map[Key, Value] k:Key --> Map[Key, Value] is void remove(K k);
        isEmpty: Map[Key, Value] is boolean isEmpty();
        contains: Map[Key, Value] k:Key is boolean containsKey(K k);
    }

end refinement