> The question I pose is this: can a point, more specifically a
> quadrapoint (quinta or even more), also be a border? Take Four
> Corners, USA for example. Is it correct to say that New Mexico and
> Utah 'border' one another? Or Arizona and Colorado?

Like you, I've puzzled over this, with reference to Jungholz and the
other exclaves that join the parent country at a single point.
My take is that the two entities don't adjoin each other at all,
since the length of their border is zero - the same as the length of
any border for any other two non-adjoining entities.
But this leaves me with an odd problem when I'm counting
international border segments around Jungholz, and other exclaves
that are joined to the parent country by a single point. From inside
Jungholz, there is a continuous border with Germany. And from
Austria, there's also a continuous border with Germany. But on the
German side, there's a discontinuity - Germany borders Austria, then
an Austrian exclave (Jungholz), then mainland Austria again.
So Germany counts three border segments, but Austria+Jungholz count
only two. Hmmm. That upsets me, so I have to revise things and say
that the border between mainland Austria and Germany is in two
discreet segments, separated by the quadripoint with Jungholz.

So that's what I think. Anyone else?

Grant