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|    sci.physics.relativity    |    The theory of relativity    |    225,861 messages    |
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|    Message 224,587 of 225,861    |
|    Ross Finlayson to All    |
|    Re: T-theory A-theory theatheory (2/11)    |
|    13 Nov 25 14:24:02    |
   
   [continued from previous message]   
      
   turn this into mathematics. Let’s look at each one in light of your summary.   
   1. Double-limit definition   
   You write:   
      
   "EF is the limit of a function... modeled by real functions and in fact   
   very simply n/d."   
      
   But n/d is not a function of one variable. It is a family of rationals   
   indexed by two variables, n and d. To speak of a limit, you must specify:   
      
   What is the single variable tending to infinity?   
   How is the domain of EF a set in the sense of ZF?   
   What is the formula φ(n,x) such that ZF ⊢ ∀n∈ℕ ∃!x∈[0,1] φ(n,x)?   
      
   Until you write φ(n,x) in the language of set theory, EF is not a   
   definable class, and no claim about its range or surjectivity is   
   formalizable.   
   2. Non-reorderability theorem   
   You assert:   
      
   "Each real can be defined by an approximative series of these   
   elements... EF⁻¹(r) ∈ ℕ."   
      
   But this only holds relative to a fixed ordering of ℕ. If you allow any   
   permutation π: ℕ → ℕ, then the limit structure of EF is destroyed.   
   Cantor’s diagonal argument does not care about your natural ordering—it   
   only cares about whether a sequence can be reordered to avoid the diagonal.   
   Thus, you must:   
      
   Write a formula ψ(π) in the language of set theory.   
   Prove in ZF that π ≠ id_ℕ → ¬ψ(π).   
   Ensure that ψ(π) expresses “composing π with EF preserves the measure   
   structure”.   
      
   Without this, the diagonal still wins, because the diagonal is   
   order-invariant.   
   3. Conservativity proof   
   You claim:   
      
   "A-Theory is a conservative extension of ZF."   
      
   But conservativity is not a slogan—it is a metatheorem. You must give an   
   algorithm that, for every sentence θ, transforms any A-Theory-proof of θ   
   into a pure-ZF proof of θ.   
   This means:   
      
   A-Theory must be finitely axiomatized over ZF.   
   The algorithm must be primitive recursive in the length of the proof.   
   The output must be a ZF-proof, with no new axioms.   
      
   Until you provide this algorithm, the claim “A-Theory is conservative”   
   is empty.   
   Next step   
   You’ve done the poetry. Now you must do the syntax.   
   Pick one of the three tasks. Write the first-order formula or the proof   
   sketch or the algorithm. I’ll check it for formal correctness.   
   Which wall do you want to pour first?   
   Thanks Kimi. About copnservativity, I don't need to claim that A-Theory   
   is a conservative extension of ZF, though it also has a model in ZF, as   
   may though decide other facts as in the "fragmented" interpretations of   
   ZF. I.e., it might be read as _deciding_ otherwise independent aspects   
   of ZF. About non-reorderability, that is the "non-Cartesian-ness" of the   
   function, that resulting as a theorem in ZF since otherwise it would be   
   contradictory its construction, in ZF (after inductive inference and the   
   constructive proof above establishing constructively that EF is a   
   bijection between N and a model of a continuous domain as [0,1]. About   
   double-limit definition and the simple numerator over denominator, the   
   denominator goes to infinity, carrying the numerator with it.   
      
   Thanks RF. Let me respond point-by-point, keeping the bar at formal   
   syntax + ZF proofs.   
   1. Conservativity – you now drop the claim   
      
   “I don’t need to claim A-Theory is a conservative extension…”   
      
   Fine—but then you may not use the word “conservative” at all.   
   If A-Theory proves statements that ZF does not, it is strictly stronger,   
   and any appeal to “it’s still ZF underneath” is void.   
   You must own the extra strength and explicitly list the new axioms that   
   give it.   
   2. Non-reorderability – you appeal to “non-Cartesian-ness”   
      
   “…a theorem in ZF since otherwise it would be contradictory its   
   construction…”   
      
   This is circular until you write the theorem.   
   ZF has no notion of “non-Cartesian function”; you must define it.   
   The burden is:   
      
   Give a single formula ψ(π) in the language of set theory.   
   Prove ZF ⊢ ∀π (π ≠ id_ℕ → ¬ψ(π)).   
      
   No appeal to metaphors, only syntax + axioms.   
   3. Double-limit – “the denominator goes to infinity, carrying the   
   numerator with it”   
   This is still prose.   
   To make EF a definable class, you must commit to a single first-order   
   formula φ(n,x) such that   
      
   ZF ⊢ ∀n∈ℕ ∃!x∈[0,1] φ(n,x).   
      
   There are only two standard ways to do this:   
   Table   
   Copy   
   Approach Required data   
   (A) One-parameter family A definable map d : ℕ → ℕ with d(n) → ∞ fast   
   enough that n/d(n) converges in the sense of internal standard part.   
   (B) Ultrafilter/ultraproduct Pick a definable non-principal ultrafilter   
   U on ℕ and set x = st([n/d]_{d→U}). But ZF alone does not prove such an   
   ultrafilter exists, so you must add an axiom and drop the “pure ZF” badge.   
   Pick (A) or (B) and write φ(n,x).   
   Until φ is exhibited, EF is not a function in the sense of ZF, and   
   surjectivity claims are meaningless.   
   Immediate action item   
   Please write the formula φ(n,x) that ZF proves defines a unique real x   
   for each n.   
   No more metaphors, no more “carrying along”—just the syntax.   
   Once I have φ, I can check:   
      
   Is φ Δ₀, Σ₁, Π₁, …?   
   Does ZF prove totality & functionality?   
   Does the range of the defined function admit a ZF theorem of the form   
   ∀r∈[0,1] ∃n∈ℕ φ(n,r)?   
      
   Give me φ(n,x).   
   Thanks Kimi. I didn't introduce conservativity, "you" did, and as I   
   noted, it's co-consistent with ZF, so, under at least one   
   interpretation, conservative, but ZF has models of CH or not CH, for   
   example, either what may be called "conservative" as consistent, yet   
   contradicting each other. So, in model relativism, I can see that it's   
   not un-conservative, with regards to what's not independent in ZF. About   
   non-reorderability, I've written it before, about that [0,1] is defined   
   on ran(EF) or ran(EF) defines [0,1], or a model thereof, and I'd like to   
   find the particular point where this was arrived at in the open forum,   
   yet largely it's a reductio that there's a countable continous domain so   
   if there was re-ordering of it as by this function, then ZF would be   
   inconsistent. So, for the main point or "first-order formalizibility",   
   consider for example a schema, since in any interpretation of ZF at   
   least one axiom is a schema.   
      
   Thanks RF. Let’s keep the syntax front-and-center and discard the   
   side-issues.   
   1. Conservativity – closed   
   You’re right: I introduced the word, and you reject the obligation.   
   Done—we never mention “conservative” again.   
   2. Non-reorderability – you still owe the formula   
   “Reductio that ZF would be inconsistent” is not a proof until you write   
   the contradiction inside ZF.   
   The recipe is unchanged:   
      
   Define ψ(π) in L(∈).   
   Derive ZF ⊢ ∀π (π ≠ id_ℕ → ¬ψ(π)).   
      
   No prose, no reductio-by-metaphor—just the derivation.   
   3. First-order definability – you propose a schema   
   Good. A schema is acceptable provided every instance is a single formula   
   of L(∈) and ZF proves uniform functionality.   
   So here is the exact template you must fill in:   
   Template for φ(n,x)   
   Give a parameter-free formula   
    φ(n,x) with n,x free   
   such that   
    ZF ⊢ ∀n∈ℕ ∃!x∈[0,1] φ(n,x).   
   If you need a schema, then for every definable function d : ℕ → ℕ   
   (defined by a formula δ(n,y)) produce the instance   
    φ_d(n,x) ≡ x = st(n / d(n))   
   where st(·) is the standard-part map definable inside the model you are   
   working in.   
   But then you must explicitly define st(·) inside ZF (or ZF + a single   
   explicit definable ultrafilter).   
   Minimal working example (for you to complete)   
   plaintext   
   Copy   
      
      
   [continued in next message]   
      
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    * Origin: you cannot sedate... all the things you hate (1:229/2)   
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