If we can know God perfectly, we can prove everything in mathematics once we fully know him and Godel's theorem will not apply. — Gregory
it is a theorem of first order logic that there is not an x such that for all y, y bears relation R to x if and only if y does not bear relation R to y. — TonesInDeepFreeze
Is this what you were referring too? — Gregory
If a theory T is a consistent, recursively axiomatizable extension of Robinson arithmetic, then there is a sentence G in the language for T such that neither G nor ~G is a theorem of T. — TonesInDeepFreeze
You can modify its form; some forms of modification are valid and some are not. I once had a form suggested to me which was not valid, namely the question whether the barber shaves himself or not. You can define the barber as "one who shaves all those, and those only, who do not shave themselves". The question is, does the barber shave himself? In this form the contradiction is not very difficult to solve. But in our previous form I think it is clear that you can only get around it by observing that the whole question whether a class is or is not a member of itself is nonsense, i.e. that no class either is or is not a member of itself, and that it is not even true to say that, because the whole form of (the?) words is just noise without meaning. — Russell
I told you what I thought of it. — Gregory
If you disagree on logic's relation to math, then start with what you think are the logical tools of Gödel's theorem — Gregory
Gödel noted that statements within a system can be represented by natural numbers. The significance of this was that properties of statements – such as their truth and falsehood – would be equivalent to determining whether their Gödel numbers had certain properties. The numbers involved might be very long indeed (in terms of number of digits), but this is not a barrier; all that matters is that we can show such numbers can be constructed.
In simple terms, we devise a method by which every formula or statement that can be formulated in our system gets a unique number, in such a way that we can mechanically convert back and forth between formulas and Gödel numbers. Clearly there are many ways this can be done. Given any statement, the number it is converted to is known as its Gödel number. — Wikipedia (Gödel numbering)
The Gödel sentence is designed to refer, indirectly, to itself. The sentence states that, when a particular sequence of steps is used to construct another sentence, that constructed sentence will not be provable in F. However, the sequence of steps is such that the constructed sentence turns out to be GF itself. In this way, the Gödel sentence GF indirectly states its own unprovability within F.
To prove the first incompleteness theorem, Gödel demonstrated that the notion of provability within a system could be expressed purely in terms of arithmetical functions that operate on Gödel numbers of sentences of the system. Therefore, the system, which can prove certain facts about numbers, can also indirectly prove facts about its own statements, provided that it is effectively generated. Questions about the provability of statements within the system are represented as questions about the arithmetical properties of numbers themselves, which would be decidable by the system if it were complete.
Thus, although the Gödel sentence refers indirectly to sentences of the system F, when read as an arithmetical statement the Gödel sentence directly refers only to natural numbers. It asserts that no natural number has a particular property, where that property is given by a primitive recursive relation. As such, the Gödel sentence can be written in the language of arithmetic with a simple syntactic form(...) — Wikipedia (Gödel incompleteness theorems)
You provided a statement and have not spoken yet of the internal logic that makes it a proof — Gregory
the law of the excluded middle. — Amalac
properties of statements – such as their truth and falsehood – would be equivalent to determining whether their Gödel numbers had certain properties. — Wikipedia (Gödel numbering)
I thought the law of the excluded middle was also needed for mathematical proofs by contradiction, like Euclid's proof that there are infinitely many primes. — Amalac
"What have I got in my pocket?" :wink:Each unprovable yet true theorem is Göd. — Agent Smith
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