On 09 May 2012, at 17:09, R AM wrote:

PM, Bruno Marchal

Yes.
"Nothing", in set theory, would be more like an empty *collection* of sets, or an empty "universe" (a model of set theory), except that in first order logic we forbid empty models (so that AxP(x) -> ExP(x) remains valid, to simplify life (proofs)).

"nothing" could also be obtained by removing the curly brackets from the empty set {}.

Noooo... Some bit of blank remains. If it was written on hemp, you could smoke it. That's not nothing!

Don't confuse the notion and the symbols used to point to the notion. Which you did, inadvertently I guess.

{ } is a set and "{ }" is a string with 3 symbols, ... which should be differentiated even from the paper and ink, or stable picture on a screen, representing physically the symbols to you, and then from the image made by your brain, and the neuronal 'music' trigged by it, and the consciousness filtered locally by the process, etc.


Or removing the (empty) container. I guess this would be equivalent to "removing" space from the universe. Except that this doesn't make any sense in Set Theory (maybe it doesn't make any sense in reality either).

Still, {} is some sort of nothing in Set Theory,

Sure, like 0 is some sort of nothing in Number theory, and like quantum vacuum is some sort of nothing in QM. Nothing is a theory dependent notion. (Not so for the notion of computable functions).

Extensionally, the UD is a function from nothing (no inputs) to nothing (no outputs), but then what a worker!

Extensionally it belongs to { } ^ { }. It is a function from { } to { }.

But that is a bit trivial, I think. It is due to the fact that computability theory is not dimensional. Dimensions also have to be derived from the internal points of view (with comp), like the real and complex numbers and the physical laws.



given that it is what is left after all that is allowed to be removed, is removed.

OK.

Bruno




Ricardo.


Bruno

http://iridia.ulb.ac.be/~marchal/

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