On 4/30/2019 11:23 AM,
tar...@google.com wrote:
> On Monday, April 29, 2019 at 10:41:40 PM UTC-7, peteolcott wrote:
>
>> Based on these three axioms Gödel's Incompleteness is refuted:
>> Axiom(1) ∀F ∈ Formal_System ∀x ∈ Closed_WFF(F) (True(F, x) ↔ (F ⊢ x))
>> Axiom(2) ∀F ∈ Formal_System ∀x ∈ Closed_WFF(F) (False(F, x) ↔ (F ⊢ ¬x))
>> Axiom(3) ∀F ∈ Formal_System ∀x ∈ Closed_WFF(F) (True(F,x) ∨ False(F,x))
>
> Not sure why these are axioms. It would seem that these are properties of
> your formal system, which if satisfied would admit it into your system. I don't
> see how asserting that all formal systems obey these axioms work. For arbitrary
> formal systems, it is clear that these axioms do not hold.
>
>> ∃F ∈ Formal_System ∃G ∈ Closed_WFF(F) (G ↔ ((F ⊬ G) ∧ (F ⊬ ¬G)))
>> There is no sentence G of Formal System F that is neither True nor False in F.
>
> I would suggest that claiming Gödel's Incompleteness is refuted is too strong a
> statement.
>
> Instead, the claim that you have is that if you create a suitably constrained
> formal system, then in *that* system you can have complete inference. This is
> well-recognized result. The interesting question is whether the constraints
> needed to achieve this complete inference will leave you with enough expressive
> power to be able to perform interesting inference in your system.
>
> Certainly one of Gödel's results is that if you have a formal system that is
> expressive enough to include arithmetic, you run into incompleteness.
Only because the mathematical system that he used to form this proof was too
weak to discern semantic ill formedness:
In the same way that not all finite strings are well-formed formula
(when semantic criteria is applied) not all closed WFF are logic sentences.
Any expression of language that is neither true nor false is
not a logic sentence of any formal system that has been
adapted to conform to the sound deductive inference model.
Logic sentences are always derived from sound deduction. In
the sound deductive inference model this means that there is:
[a connected sequence of valid deductions from true premises to a true conclusion].
When axioms are construed as expressions of language having the
semantic property of Boolean true then the theorem consequences
of formal proofs form:
[a connected sequence of inference from axioms to a true consequence].
In neither case is undecidability, incompleteness or inconsistency possible.
>A
> consequence of that is that your system, therefore, cannot use arithmetic. As
> long as you don't need arithmetic for the inferences of interest, then you may
> find your formal system adequate.
>
> For an interesting discussion of some issue having to do with decidability and
> efficiency of reasoning, you may want to look at the Description Logic
> research. There are a number of variants of description logic with different
> expressive power and consequently different decisions regarding what can be
> computed, ranging from tractable complete inference to undecidability.
>
> Overview:
https://en.wikipedia.org/wiki/Description_logic
> Complexity:
http://www.cs.man.ac.uk/~ezolin/dl/