public static PositionBound unbounded() {
        return new PositionBound(Position.emptyPosition());
    }
@Test
    public void shouldEqualUnbounded() {
        final PositionBound bound1 = PositionBound.unbounded();
        final PositionBound bound2 = PositionBound.unbounded();
        assertEquals(bound1, bound2);
    }