is, since the first and last terms
    are also open.

JA: Not sure.  I'm still in the muddle o' medias res myself.
    But I do have a passel of charts and graphs on this bit,
    which you just know you're gonna get to see.  But just
    for teaser of coming attractions, look at this picture:

JA: |          Z
    |          o
    |          |\
    |          | \
    |          |  \
    |          |   \
    |          |    \  Rule
    |          |     \
    |          |      \
    |          | A   &gt; \
