William White <bwhite(at)frognet(dot)net> writes:
> Consider the empty interval (n,n) (any empty interval will do, they're
> all the same empty set),
I don't think that's the case. [0,0) and [1,1) are certainly
distinguishable given the normal machine representation of intervals.
If you use a mathematical model that says they're not distinguishable,
that says to me that you chose the wrong model --- especially when the
model leads you into logical difficulties that need not (and do not)
exist in the actual implementation.
My feeling about it is [0,0) << [1,1) but not vice versa.
regards, tom lane