Do we have implicit semi-infinites...?

[Dan Zuras Intervals <intervals08@xxxxxxxxxxxxxx>]

	Folks,

	I have been contemplating that split function we discussed
	earlier.  In so far as is possible, I would like to write
	it independent of the underlying interval form.  In effect,
	not caring whether one uses explicit (inf-sup or [a,b] form)
	or implicit (mid-rad or <m,r> form).

	But I am running up against the differences in the set of
	intervals these two forms can represent.  Specifically, I
	need to know something about how (or whether) implicit forms
	will represet semi-infinite intervals.

	How does one (or can one) represent a semi-infinite interval
	of the explicit form [a,+inf] as an implicit <m,r>?

	Can one represent Entire?  Perhaps as <0,+inf>?

	Can one use r = +inf at all?

	Can one represent Empty?  Say <0,-inf>?

	Can one use r < 0 at all?

	Or have these things been decided yet?

	Anything you can tell me...

	Thanks,

				   Dan