@Override
    public R get(Object key) {
        if (key instanceof Integer) {
            int n = (Integer) key;
            return get(n);
        }
        return super.get(key);
    }
@Test
    public void lookup() {
        assertNull(a.get(0));
        a.get(1).asserts(1);
        assertNull(a.get(2));
        a.get(3).asserts(3);
        assertNull(a.get(4));
        a.get(5).asserts(5);
        assertNull(a.get(6));

        assertNull(b.get(1));
        assertNull(b.get(3));
        assertNull(b.get(5));
    }