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|    Message 262,726 of 262,912    |
|    olcott to Richard Damon    |
|    Re: The Halting Problem asks for too muc    |
|    25 Jan 26 12:33:30    |
      XPost: sci.math, comp.theory       From: polcott333@gmail.com              On 1/25/2026 12:27 PM, Richard Damon wrote:       > On 1/25/26 8:24 AM, olcott wrote:       >> On 1/25/2026 5:19 AM, Mikko wrote:       >>> On 24/01/2026 16:01, olcott wrote:       >>>> On 1/24/2026 2:20 AM, Mikko wrote:       >>>>> On 23/01/2026 12:22, olcott wrote:       >>>>>> On 1/23/2026 3:13 AM, Mikko wrote:       >>>>>>> On 22/01/2026 18:40, olcott wrote:       >>>>>>>> On 1/22/2026 2:21 AM, Mikko wrote:       >>>>>>>>> On 21/01/2026 17:22, olcott wrote:       >>>>>>>>>> On 1/21/2026 3:03 AM, Mikko wrote:       >>>>>>>>>>>       >>>>>>>>>>> No, it hasn't. In the way theories are usually discussed       >>>>>>>>>>> nothing is       >>>>>>>>>>> "ture in arithmetic". Every sentence of a first order theory       >>>>>>>>>>> that       >>>>>>>>>>> can be proven in the theory is true in every model theory. Every       >>>>>>>>>>> sentence of a theory that cannot be proven in the theory is       >>>>>>>>>>> false       >>>>>>>>>>> in some model of the theory.       >>>>>>>>>>>       >>>>>>>>>>>> only because back then proof theoretic semantics did       >>>>>>>>>>>> not exist.       >>>>>>>>>>>       >>>>>>>>>>> Every interpretation of the theory is a definition of semantics.       >>>>>>>>>>>       >>>>>>>>>>       >>>>>>>>>> Meta‑math relations about numbers don’t exist in PA       >>>>>>>>>> because PA only contains arithmetical relations—addition,       >>>>>>>>>> multiplication, ordering, primitive‑recursive predicates       >>>>>>>>>> about numbers themselves—while relations that talk about       >>>>>>>>>> PA’s own proofs, syntax, or truth conditions live entirely       >>>>>>>>>> in the meta‑theory;       >>>>>>>>>       >>>>>>>>> Methamathematics does not need any other relations between numbers       >>>>>>>>> than what PA has. But relations that map other things to numbers       >>>>>>>>> can be useful for methamathematical purposes.       >>>>>>>>>       >>>>>>>>>> so when someone appeals to a Gödel‑style relation like       >>>>>>>>>> “n encodes a proof of this very sentence,” they’re       >>>>>>>>>> invoking a meta‑mathematical predicate that PA cannot       >>>>>>>>>> internalize, which is exactly why your framework draws       >>>>>>>>>> a clean boundary between internal proof‑theoretic truth       >>>>>>>>>> and external model‑theoretic truth.       >>>>>>>>>       >>>>>>>>> Anyway, what can be provven that way is true aboout PA. You can       >>>>>>>>> deny       >>>>>>>>> the proof but you cannot perform what is meta-provably impossible.       >>>>>>>>       >>>>>>>> Gödel’s sentence is not “true in arithmetic.”       >>>>>>>> It is true only in the meta‑theory, under an       >>>>>>>> external interpretation of PA (typically the       >>>>>>>> standard model ℕ). Inside PA itself, the sentence       >>>>>>>> is not a truth‑bearer at all.       >>>>>>>       >>>>>>> There is no concept of "truth-bearer" in an uninterpreted theory       >>>>>>> because       >>>>>>> there is not concept of "truth". The relevant concept is "sell-       >>>>>>> formed-       >>>>>>> formula" and Gödels sentence is one. It may be true or false in an       >>>>>>> interpretation.       >>>>>       >>>>>> There is a       >>>>>> "true on the basis of meaning expressed in language"       >>>>>> and I figured out how to make it computable over the       >>>>>> body of knowledge.       >>>>>       >>>>> Except that "true on the basis of meaning expressed in language" is       >>>>> nmt computable and does not cover all of the body of knowldge.       >>>>       >>>> When the basis of "true" is proof theoretic semantics       >>>> internal to the formal system relative to its own axioms       >>>> and not truth conditional in a separate model outside       >>>> of the system undecidability ceases to exist.       >>>       >>> No, it does not. It does not matter what you call it, a sentence       >>> that cannot be neither proven nor disproven is undecidable because       >>> that is what the word means. An example is Gödel's sentence in       >>> Peano arithmetics.       >>>       >>       >> When a truth predicate gets the input "What time is?"       >> this input is rejected as not truth-apt.       >       >       > That fine.       >>       >> When PA gets an expression that cannot be proven or       >> refuted using its own axioms then this expression is       >> not within its domain.       >>       >       > Then most of Natural Number mathematics is isn't in its domain,       >              It is what it is.       PA doesn't even know PA until you add a truth predicate.       When you do add a truth predicate then PA knows PA. If       you want more than that then meta-math can know "about" PA.       This is one level of indirect reference away from knowing PA.              > And, you can't KNOW if somehting is a valid question to ask until you       > know the answer.       >       > This makes a fairly worthless domain to learn things in.       >       > By your definition, a question like can every even number, greater than       > 2, be the sum of two prime numbers MIGHT not be within its domain, even       > though it is purely a question about the capability of numbers.       >                     --       Copyright 2026 Olcott |
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