Zero size areas/volumes do not overlap and are not contained

[io7m]

This is a serious issue:

  @Test
  public void testBugOverlapsL()
  {
    final AreaL area0 =
      AreaL.of(0L, 10L, 0L, 10L);
    final AreaL area1 =
      AreasL.create(0L, 0L, 0L, 0L);
    Assert.assertTrue(AreasL.overlaps(area1, area0));
  }

... fails!

[io7m]

Actually containment seems to work correctly:

  @Test
  public void testBugContainsL()
  {
    final AreaL area0 =
      AreaL.of(0L, 10L, 0L, 10L);
    final AreaL area1 =
      AreasL.create(0L, 0L, 0L, 0L);
    Assert.assertTrue(AreasL.contains(area0, area1));
  }

[io7m]

This is a little philosophical. Can an area of zero height and/or width be said to overlap anything? By definition, it has zero size...

If the assumption is that an area of zero size cannot overlap, however, then ∀a. overlaps(a, a) doesn't necessarily hold. Might it make sense to treat an area of zero size as a point?

[io7m]

It seems like the easiest way to handle this is to make the width and height of the boxes at least 1 when performing the overlap checks. I can't see anything obviously wrong with doing this, it makes the mathematics work, and it doesn't seem to violate any of the existing theorems.