    @Test
    public void testEquals2() {

        assertEquals(AHashSet.empty (),
                     AHashSet.empty ());
        assertEquals(AHashSet.empty ().with("a"),
                     AHashSet.empty ().with("a"));
        assertEquals(AHashSet.empty ().with("a").with("b"),
                     AHashSet.empty ().with("b").with("a"));

        assertNotEquals(AHashSet.empty (),
                        AHashSet.empty ().with("a"));
        assertNotEquals(AHashSet.empty ().with("a"),
                        AHashSet.empty ());
        assertNotEquals(AHashSet.empty ().with("a").with("b"),
                        AHashSet.empty ().with("a").with("b").with("c"));
        assertNotEquals(AHashSet.empty ().with("a").with("b").with("c"),
                        AHashSet.empty ().with("a").with("b"));
        assertNotEquals(AHashSet.empty ().with("a").with("b").with("c"),
                        AHashSet.empty ().with("b").with("c"));

        assertNotEquals(AHashSet.empty (), null);
    }