# Re: Proposal: 6NF

Date: 19 Oct 2006 02:17:11 -0700

Message-ID: <1161249431.916955.140240_at_m7g2000cwm.googlegroups.com>

Marshall wrote:

> On Oct 18, 3:15 pm, "dawn" <dawnwolth..._at_gmail.com> wrote:

*> > A nit, perhaps, but which values would those be that we cannot
**> > represent with computers?
**>
**> I would be hard pressed to figure out how to represent an
**> uncomputable number with a computer. Unless we give it a
**> name like, say, "Fred" and store "Fred" as a string.
**> But then we're representing the name of the value, and
**> not the value itself.
*

Indeed, the question should not be "which value cannot be represented in a computer" (because any value can by just defining a certain symbol to mean that value) but "which sets of values cannot be represented in a computer". The answer to that is an obvious "any finite or countably infinite set". It becomes more interesting if the set you are talking about must have certain operations defined over it because then, in addition, these operations, including equality, must be computable over the chosen representation. For the recursive reals this is possible, but if you add one uncomputable real to the set the operations become uncomputable.

- Jan Hidders