Issue: SUBTYPEP-EMPTY-NIL (Version 1)

[Glenn S. Burke <gsb@ALDERAAN.SCRC.Symbolics.COM>]

    Date: Wed, 8 Feb 89 09:37 EST
    From: Kent M Pitman <KMP@STONY-BROOK.SCRC.Symbolics.COM>

    Sorry, but this is a serious attempt to get a clarification.

    I don't see that any criterion has been advanced by CLtL for believing
    NIL T is any better or worse than T T.  If CLtL is clear and I've just
    missed the passage, by all means cite it.  Alternatively, you may have some
    personal criterion which you'd like us to buy into. If you propose that
    criterion and no one contests, I'll be quite happy to see the issue
    turn out to resolved by a non-controversial vote.

NIL T leads to a situation of functionally equivalent forms of the "empty"
type set not being equivalent under (and (subtypep x y) (subtypep y x)).
I believe that to be a good argument for T T, whether or not CLtL even
hints that this should be the case.