On Oct 7, 7:55 pm, Graham Cooper <
grahamcoop...@gmail.com> wrote:
> On Oct 8, 9:25 am, Charlie-Boo <
shymath...@gmail.com> wrote:
>
>
>
>
>
> > On Oct 7, 5:37 pm, Graham Cooper <
grahamcoop...@gmail.com> wrote:
> > > > > On Oct 7, 6:32 am, Paul <
pepste...@gmail.com> wrote:
>
> > > > > > David Ullrich used to append this quotation to his newsgroup postings:
>
> > > > > > "Understanding Godel isn't about following his formal proof.
> > > > > > That would make a mockery of everything Godel was up to."
>
> > > > > > Since I'm obsessed with following in full detail a rigorous account of Godel's theorems (I've yet to find one online which has the detail I want and where I don't get stuck on one of the steps), then obviously I must be doing completely the wrong thing, ullrichistically speaking.
>
> > > > > > If following his formal proof is the wrong way to understand Godel, then what is a better way to understand Godel?
>
> > > > > > Thank You,
>
> > > > > > Paul Epstein
>
> > > > > Beware the difference between GODELS PROOF
> > > > > and MATHEMATICS ABOUT GODELS PROOF.
>
> > > > > The latter is a lot more convoluted and not necessary to 1st follow
> > > > > the proof itself.
>
> > > > “It is an error to believe that rigour is the enemy of simplicity. On
> > > > the contrary we find it confirmed by numerous examples that the
> > > > rigorous method is at the same time the simpler and the more easily
> > > > comprehended. The very effort for rigor forces us to find out simpler
> > > > methods of proof.” - David Hilbert, 'Mathematical Problems', Bulletin
> > > > of the American Mathematical Society (Jul 1902), 8, 441
>
> > > > “18 Word Proof of the Godel, Rosser and Smullyan Incompleteness
> > > > Theorems”
http://www.cs.nyu.edu/pipermail/fom/2010-July/014890.html
>
> > > > > T1|-!(PRV(GS-GN)) & T2|-PRV[ T1|-!(PRV(GS-GN)) ]
>
> > > > > !PRV(GS-GN) is true in THEORY 1
> > > > > and
> > > > > that fact is proven in THEORY 2.
>
> > > > > GS = !PRV(GS-GN) *a Godel Statement
>
> > > > What are T1, PRV, GS-GN, T2, THEORY 1, THEORY 2 and GS? What is the
> > > > purpose of displaying these expressions?
>
> > > EXACTLY MY POINT!
>
> > What is exactly your point? I asked you to define the elements of
> > your expressions and you don;t answer me and then say you agree with
> > something.
>
> I quoted my point directly after.
>
> When people DISCUSS Godel's proof they use formula such as
>
> T |- G
>
> In Theory T, G is a Theorem
>
> My point being this is commonly confused for Godel's Proof itself.
>
>
>
> > What are T1, PRV, GS-GN, T2, THEORY 1, THEORY 2 and GS? What is the
> > purpose of displaying these expressions?
>
> In Godel's Proof the Godel Statement GS
> is true in one Theory T1
> and proven in a seperate Theory T2
>
> NOTE: this is talking ABOUT Godel's proof,
> not PART of the proof.
>
>
>
>
>
>
>
> > > Beware the difference between GODELS PROOF
> > > and MATHEMATICS ABOUT GODELS PROOF.
>
> > > > > Also beware the phrase
> > > > > "IN ANY THEORY WITH SUFFICIENT EXPRESSIVENESS..
> > > > > ..WE CAN CONSTRUCT THIS SENTENCE ..."
>
> > > > Ironically, they say that exactly because they have not formalized
> > > > it. They don’t know what the actual premise is, and so they use a
> > > > meaningless phrase “sufficiently expressive”.
>
> > > > > That only holds for ZERO-AXIOM or INCONSISTENT systems where ALL (true
> > > > > and false) theorems follow.
>
> > > > It holds for any system in which we can express “x is the number of a
> > > > provable sentence”, and the premise (soundness or w-consistency) is
> > > > true, depending on the version being cited from his 1931 paper. Both
> > > > hold for ordinary Peano Arithmetic.
>
> > > NO!
>
> > Can you prove that? Can you give a system in which provability is
> > expressible and there is no undecidable sentence?
>
> Aye Curumba!
>
> > If we can express "wff x is provable", then we can express "wff x with
> > x substituted for its free variable is not provable". Let w(x)
> > express that
>
> NO!
w is S in Godel's article. What is S if not w?
"We will assume the class-signs are somehow numbered, call the nth one
Rn. . . . Now we will define a class K of natural numbers as follows:
K = { n e N| ~provable(Rn(n)) } (where provable(x) means x is a
provable formula).
Since the concepts which appear in the definiens are all definable in
PM, so too is the concept K which is constituted from them, i.e.
there is a class-sign S such that the formula [S; n]—interpreted as to
its content—states that
the natural number n belongs to K."
http://jacqkrol.x10.mx/assets/articles/godel-1931.pdf
> Also beware the phrase
>
> "IN ANY THEORY WITH SUFFICIENT EXPRESSIVENESS..
> ..WE CAN CONSTRUCT THIS SENTENCE ..."
>
> .
>
>
>
>
>
>
>
> > Define TW(x,y) to be wff x with y substituted for its free variable is
> > true, and PR likewise but it's provable. Let M be the Godel number of
> > w.
>
> > TW(M,x) is true means w(x) is true means ~PR(x,x). Then TW(M,M) iff
> > ~PR(M,M) and TW does not coincide with PR. So a sentence is false and
> > provable (but that would not be SOUND) or true and unprovable. Let W
> > be true and unprovable. Then if ~W is provable then, again by
> > soundness, it is false, but it is true, so ~W is not provable and W is
> > undecidable.
>
> > > TARSKI makes the EXACT SAME ERROR as GODEL
>
> > > [DARYL]
> > > Fix a coding for arithmetic, that is, a way to associate a unique
> > > natural number with each statement of arithmetic. In terms of this
> > > coding, a truth predicate Tr(x) is a formula with the following
> > > property: For any statement S in the language of arithmetic,
> > > Tr(#S) <-> S
> > > holds (where #S means the natural number coding the sentence S).
> > > If Tr(x) is a formula of arithmetic, then using techniques
> > > developed by Godel, we can construct a sentence L such that
> > > L <-> ~Tr(#L)
> > > But by the definition of a truth predicate, we also have
> > > L <-> Tr(#L)
>
> > That is Tarski's Undefinability Theorem. What is the point?
>
> > > NOTICE THE "we can construct a sentence L"
>
> > > *a* sentence means *any* sentence here.
>
> > > START WITH AN INCONSISTENT THEORY
>
> > > then using techniques developed
> > > by Godel, we can construct *ANY* sentence L
>
> > > T |- W
> > > T |- L
> > > T |- L<->~G2T(L) *IN T |- W ANY FORMULA IS TRUE
> > > T |- L<->G2T(L)
> > > T |- L , T |- ~L *contradiction
> > > T |- W *now any formula is true
>
> > What are T, W, L and G2T? Again you are displaying expressions with
> > undefined primitives. What is this supposed to represent? Is this
> > supposed to be a proof of something?
>
> > What is the point of displaying expressions without definitions of
> > their symbols in a list? You start with T |- W and end with the same
> > expression T |- W but the 2nd time you add "*now any formula is
> > true". Why do you have to list it as if it were derived twice? Are
> > you meaning that T is a set of axioms and W is provable from them?
> > But you haven't define T or W or the other primitives e.g. G2T.
>
> > What are you trying to say?
>
> > > Yeh so?
>
> > > *************************
>
> > > For any Theory T and it's Theorems t1, t2,t3,...
>
> > > T |- t1 ^ t2 ^ t3 ^ t4 ^ ....
>
> > > t3 <-> ~true(#t3)
>
> > Since t3 is a theorem then it will be true by soundness, a premise
> > made in one version of Godel's theorem.
>
> > How do you justify this statement about t3? You haven't mentioned t3
> > before. Is this supposed to be true of all theorems?
>
> > > t3 <-> not(t3)
> > > IS CONSTRUCTABLE
>
> > What is not constructable?
>
> > Your writings are quite mysterious! Maybe if you defined what the
> > various variable names represent it would add some meaning to these
> > expressions.
>
> > C-B
>
> T |- W
>
> A theory T that derives all formula, Omega, Infinity.
>
> t1 ^ ~t2 |- W
>
> From a contradiction all formula can be derived.
>
> *****************
>
> PUT IT SIMPLY
>
> *****************
>
> YOU CAN NOT ADD ANY FORMULA TO ANY THEORY
>
> Herc