public int floor(T v) {
        return Boundary.FLOOR.apply(find(v));
    }
@Test
    public void testFloor() {
        assertEquals(-1, l.floor("A"));
        assertEquals(0, l.floor("B"));
        assertEquals(0, l.floor("C"));
        assertEquals(1, l.floor("D"));
        assertEquals(1, l.floor("E"));
        assertEquals(2, l.floor("F"));
        assertEquals(2, l.floor("G"));
    }