Incompleteness Without Infinity

\chgtext{Gödel’s incompleteness theorems are widely read as evidence against finitism. This paper examines the phenomenon under a finite ontology and argues that the reading is mistaken. Over a fixed finite structure the hypotheses of the theorems fail, and the structure’s theory is complete and decidable; the phenomenon then decomposes rather than vanishes.
Every machine check is exact: an exhaustive enumeration or an integer computation, with no floating point. Where a check works on a fixed sample, its label says so. Each cited Lean declaration proves the step its own docstring names. In each library the declaration named by a row’s key is the conjunction of the theorems the row cites there. A cited definition is named in its docstring. The closing paragraph says what these steps cover. The corpus master ledger lists A4 under its row 00:A2, D1 under A5 and D3 under A6. It lists C2, C3 and G7 under Z1, and F2, F6 and G5 under Z9. Its rows 00:A3, 00:Z2 and 00:Z3 also name this paper, and no row of this ledger is listed under them.
#DescriptionStatus Sources
A. Inputs
A1p25001The classical theorems, used as proved: Gödel’s first and second incompleteness theorems with Rosser’s strengthening, Tarski’s undefinability of truth, the essential undecidability of $\mathsf{Q}$ and of $\mathrm{R}$, Gödel’s speed-up. No classical derivation is disputed.I
[G"odel 1931; Rosser 1936; Tarski 1936; Tarski 1956; Tarski et al. 1953; G"odel 1936]
A2p25002Model theory, classical results used as proved. Trakhtenbrot: validity over the class of all finite structures is not recursively enumerable. Presburger arithmetic is complete and decidable. Second-order Peano arithmetic is categorical under full semantics (Dedekind). Second-order arithmetic truth is not arithmetical.I
[Trakhtenbrot 1950; Libkin 2004; Presburger 1930; Shapiro 1991; V"a"an"anen 2001]
A3p25003Proof complexity and bounded arithmetic, used as proved. Polynomially bounded proof systems are tied to the hard-tautologies problem, and superpolynomial lower bounds hold for specific weak systems. Pudlák bounds finite consistency statements and frames the finite-domain programme. The row also imports feasibility, bounded arithmetic, Chaitin’s information bound and partial truth definitions.I
A4p25004The corpus: effective determinacy characterises the finite structures, proved also as 5:D8. No bounded agent certifies that its universe is infinite: every bounded record consistent with an infinite domain is realised in all sufficiently large finite structures. The master rows naming this paper as a source are 00:A3, 00:A4, 00:A4, 00:Z1–00:Z3 and 00:Z9.I
master: 00:A2
B. Structures, agents and grades of decision
B1p25005The setting: a structure $\M$ in a finite signature $\sigma$ with $\lvert\M\rvert=m\ge2$ finite. $L$ is its first-order language, and $\varphi\in\Th(\M)$ abbreviates $\M\models\varphi$, likewise $\ThSO(\M)$ for second-order sentences under full semantics. The running example is $\M_p=(\{0,\dots,p-1\};0,1,+,\times)$, arithmetic modulo a prime. Rows E1, F7, F8, G5 and G8 are stated over $\M_p$.D
Section 2
B2p25006Iteration and induction: iteration names the successor act, total on a finite cycle, where it wraps. “Unbounded iteration” abbreviates the freshness claim, a successor injective and never returning to zero. Induction names the proof principle. The two are independent. A finite ontology keeps induction and the act, and declines the freshness claim.D
Section 2
B3p25007The agent: capacity $(K,H)$ over an alphabet of $a\ge2$ letters, at most $K$ symbols of storage and $H$ elementary steps. A derivation system $\D$ is sound, its steps locally checkable with checking polynomial $p_{\D}$. A certificate is a retained, step-checked record of a $\D$-derivation with one designated end sentence, of length at most $B=\min(K,H)$.D
Def. 2.1
B4p25008Local soundness: a rule is locally sound if it preserves truth in every structure that agrees with $\M$ on the table entries its check consults. An axiom rule is locally sound when its sentence is true in every such structure. An axiom asserted on syntactic recognition consults nothing.D
Def. 2.1
B5p25009Grades of decision. (i) A truth value and nothing more. (ii) A decision specified as a finite evaluation object over the tables, of computed size on the order of $m^{q}$ at quantifier depth $q$. (iii) Certification by an agent within its budget. A sentence is in the reach gap when decided at grade (ii) and not at grade (iii).D
Def. 2.2
C. Gödel’s hypotheses over a finite structure
C1p25010No finite structure interprets $\mathsf{Q}$: a model of $\mathsf{Q}$ has an injective successor with $0$ outside its range, and on a finite set an injective map is onto.T
python sourceLean, the coreLean, Mathlib
Prop. 3.1
master: 00:Z1
C2p25011Completeness and decidability: for finite $\M$ the theory $\Th(\M)$ is complete, consistent and decidable by exhaustive evaluation. A sentence of quantifier depth $q$ takes at most $c\,m^{q}$ atomic evaluations, $c$ depending on its length. One first-order sentence $\sigma_{\M}$ characterises $\M$ up to isomorphism.T
python sourceLean, Mathlib
Prop. 3.2
master: 00:Z1
C3p25012Vacuity: over a fixed finite $\M$ neither incompleteness theorem has an instance. $\Th(\M)$ is consistent, effectively axiomatisable and complete. The hypothesis that fails is the interpretation of $\mathsf{Q}$ (C1). No sentence true in $\M$ is undecided by $\Th(\M)$.T
Cor. 3.4; C1, C2
master: 00:Z1
C4p25013Trakhtenbrot’s theorem concerns validity over the class of all finite structures. The finite ontology examined here commits to one structure, not to the class. For a fixed $\M$ row C2 applies and no undecidability enters.D
Rem. 3.3; C2
master: 00:Z1
C5p25014Tarski scoped: the $m+1$ sentences $\varphi,\neg\varphi,\dots,\neg^{m}\varphi$ outnumber the $m$ elements of $\M$, so every numbering of the sentences by elements of $\M$ gives two of them the same number. Truth in $\M$ is defined externally by a finite table with the evaluation procedure of C2. What fails is the internalisation of truth.T
python sourceLean, the coreLean, Mathlib
Rem. 3.5; C2
D. The part cannot hold the whole
D1p25015Relational diagonal: an agent of storage capacity $K$ with $a^{K}<m$ has no injective encoding of the elements of $\M$ into its storage states. Every internal representation identifies distinct elements. A fortiori the agent holds no faithful model of $\M$ that also represents the model’s own encoding map.T
python sourceLean, the coreLean, Mathlib
Thm. 4.1
master: 00:A4
D2p25016The limitation relocated: the diagonal’s limitative role passes from the provability of truths to the representability of the totality by a part. Tarski undefinability relocates the same way in its representational face: truth of $\M$ is externally a table, internally unrepresentable by a smaller part.D
Rem. 4.2
master: 00:A4
D3p25017Wrap, aliasing: every total assignment of storage readings to the elements of $\M$ identifies distinct elements when $a^{K}<m$. Some reading stands for at least $\lceil m/a^{K}\rceil\ge2$ elements. Every element outside a maximal faithfully represented range is read as an alias of one inside it.T
python sourceLean, Mathlib
Lem. 4.3(1)
master: 00:A4
D4p25018Wrap, no internal trace: the steps that verify a certificate succeed in a finite $\M'$ built on its cited table entries, $\lvert \M'\rvert\le(r+1)\,p_{\D}(B)$, $r$ the largest arity. Under locally sound rules its end sentence is true there. An axiom asserted on syntactic recognition transports as a record, not as a truth. If $(r+1)\,p_{\D}(B)\le a^{K}$, no certificate marks a reading exact.T
python sourceLean, the core
Lem. 4.3(2)
E. The reach bound
E1p25019Abundance: the closed terms over $\{1,+\}$ with $\ell$ leaves are the full binary trees, $C_{\ell-1}\ge2^{\ell-2}$ in number. In $\M_p$ all have the value $\ell\bmod p$, so any two give a true equation of length $O(\ell)$, at least $2^{\ell}$ of them for $\ell\ge6$. The true sentences of length at most $L$ number at least $2^{\alpha L}$ for large $L$, $\alpha>0$ constant.T
python sourceLean, the coreLean, Mathlib
Lem. 5.1
E2p25020Vanishing reach: an agent of capacity $(K,H)$ certifies at most $a^{B+1}$ sentences over all its runs, the records being strings of length at most $B$. The certified fraction of the truths of length at most $L$ (E1) is at most $a^{B+1}/2^{\alpha L}$, below $1/N$ as soon as $\alpha L>(B+1)\log_2a+\log_2N$.T
python sourceLean, the coreLean, Mathlib
Prop. 5.2; E1
E3p25021Possession: certification is possession under the retention clause. Holding a schema and a derivation procedure is holding two records, not the instances. An instance is possessed exactly when its own certificate is retained.D
Rem. 5.3
E4p25022A single hard sentence, system-relatively: the bare evaluation calculus infers $\forall x\,\varphi(x)$ from the $m$ premises $\varphi(c)$. Every derivation of a global clause there has length at least $m$ and defeats every budget $H<m$. A richer $\D$ may derive some global clauses briefly.T
python source
Rem. 5.4
F. The diagonal under finitude
F1p25023Mention cost: if the truth of a formula in $\M$ depends on coordinate $i$ of a tuple of variables, then $v_{i}$ occurs in it. A formula whose truth depends on all $N$ coordinates has length at least $N$. A quantifier block binding an $N$-tuple contributes at least $N$ symbols.T
python sourceLean, the core
Lem. 5.5
F2p25024No compression: code strings of length at most $N$ as tuples in $\M^{N}$, one coordinate per symbol, signature and alphabet fixed independently of $N$, $\theta$ non-degenerate. The Gödel template has no instance at any scale. The diagonal formula needs $\lvert \delta\rvert\ge3N+\lvert \theta\rvert>N$ symbols, so its code is not in $\M^{N}$. Splitting the scales fails: $\delta$ outgrows the scale $\theta$ reads.T
python sourceLean, the core
Thm. 5.6; F1
master: 00:Z9
F3p25025Quotation exceeds mention: a formula’s arity is below its length. No sentence $\lambda$ contains a subformula whose truth depends on all coordinates of a tuple of arity at least $\lvert \lambda\rvert$. Under any coding that spends at least $\lvert \lambda\rvert$ coordinates on $\lambda$, per-symbol coding included, no sentence’s truth is sensitive to every coordinate of its own code.T
python sourceLean, the core
Cor. 5.7; F1
master: 00:Z9
F4p25048Density: $m$ has $d$ base-$a$ digits. An injective coding of length-$n$ strings by $k$-tuples, $k\ge1$, needs $m^{k}\ge a^{n}$, so $n<dk$. In F2’s $\delta(u)=\exists v\,(\mathrm{Diag}(u,v)\wedge\theta(v))$ let $v$ have $k$ coordinates and $u$ have $k_{1}$. Each coordinate of $v$ is named three times, each of $u$ once. So $\lvert\delta\rvert\ge2c(k)+c(k+k_{1})$, and $\lambda=\delta(\ulcorner\delta\urcorner)$ has $\lvert\lambda\rvert\ge3c(k)+k_{1}$, $c(j)$ the total length of the $j$ shortest names.T
python sourceLean, the coreLean, Mathlib
Lem. 5.8; F2
F5p25027What the construction consumes: classically, one variable over an unbounded arithmetic carries a code of any size at constant syntactic cost. Over a fixed finite structure it carries one element’s digits. Gödel’s proof uses infinity as a syntactic resource, the exponential compression of quotation. Row F2 concerns the construction, not material biconditionals, and does not diminish the classical result.D
Rem. 5.13
F6p25047The threshold lies inside the count: the code of $\delta$ fills $u$, that of $\lambda$ fills $v$. By F4 the template needs $2c(k)+c(k+k_{1})<dk_{1}$ and $3c(k)+k_{1}<dk$. Let $k^{*}(\M)$ be the largest such $k$, or $0$ if none, and $t(\M)=d\,k^{*}(\M)$. No instance codes $\lambda$ at length $n\ge t(\M)$, and $t(\M)<m$ in every structure. $k^{*}(\M)<6a^{\lfloor d/3\rfloor+1}$, and $k<6a^{\lfloor d/4\rfloor+1}$ at one scale, $k_{1}=k$.T
python source
Lem. 5.8; F4
master: 00:Z1, 00:Z9
F7p25049Decoders: over $\M_p$ with $+$, $\times$, $0$ and $1$, a formula $\mathrm{Int}_{J}(x)$ of $50J+29$ symbols in the syntax of F8 defines $\{0,\dots,2^{J}-1\}$ when $2^{J}\le p$. It writes the binary expansion with six bound variables, four of them reused. A formula $\mathrm{Dig}(y,r,s)$ defines digit $r$ of $y<\beta^{n}$ in base $\beta=2^{b}$ when $2^{bn+1}<p$, at a length linear in $bn$.T
python source
Lem. 5.9
F8p25050A dense-coded instance: alphabet of $32$ symbols, constants $0,\dots,16$, $D=1024$ symbols per element, $k_{1}=4096$, $k=45044$, $p$ of at least $D+2$ digits in base $32$. For every $\theta(v)$ of at most $704\,170$ symbols without variables of $u$, a formula $\mathrm{Diag}$ defines diagonal substitution on strings with the layout of $\delta$, and $\lvert\delta\rvert\le Dk_{1}$, $\lvert\lambda\rvert\le Dk$, $\M_p\models\lambda\leftrightarrow\theta(\ulcorner\lambda\urcorner)$.T
python source
Thm. 5.10; F2, F7
master: 00:Z9
G. What stands in the diagonal’s place
G1p25028Length horizon: a certificate contains its designated end sentence, so no sentence longer than $B=\min(K,H)$ is certifiable. None longer than $H$ has a derivation of length at most $H$ in any system. Beyond every budget there are truths, by counting alone (E1, E2).T
python source
Prop. 5.14; E1, E2
G2p25029The evaluation ceiling: without the local-checkability clause the one-rule system $\D_{\mathrm{tt}}$ asserts $\varphi$ outright on exhaustive evaluation. It is sound, and every true $\varphi$ has a derivation of length $\lvert \varphi\rvert$. So a truth lacks a derivation of length at most $H$ exactly when it is longer than $H$. The step-check of $\D_{\mathrm{tt}}$ costs on the order of $m^{q}$ evaluations.T
python source
Prop. 5.15
G3p25030The complexity remainder: whether every sound, locally checkable $\D$ leaves short truths underivable at every budget is the hard-tautologies problem, open in general and proved for specific weak systems. For bounded consistency, certificates below $H^{\varepsilon}$ are excluded where Pudlák’s bounds hold, and the budget-$H$ analogue is open. The status is the same on both ontologies.I
Rem. 5.16; A3
master: 00:Z1
G4p25031Prefix simulation: $Q_{1}z_{1}\cdots Q_{d}z_{d}\,\psi(\bar z)$ holds in $\M$ exactly when $\forall y_{1}\exists x_{1}\cdots\forall y_{d}\exists x_{d}\,[\bigwedge_{i:Q_{i}=\forall}x_{i}=y_{i}\wedge\psi(\bar x)]$ does: one uniform prefix simulates every coded quantifier pattern.T
python sourceLean, the core
Lem. 5.17
G5p25032Fragment truth is definable over $\M_p$ with $p\ge a+1$, in the expansion $L_{A}$ of $L$ by alphabet-code constants. For each $n$ of $s$ digits a formula $\mathrm{Truth}_{n}(v)$ of length $O(n^{2}s)$ defines truth for the coded prenex sentences of length at most $n$. It rejects every other code. It guesses parse and evaluation labels, checked by local clauses under G4’s prefix.T
python source
Thm. 5.18; G4
master: 00:Z9
G6p25033What remains undefinable: no single formula defines truth across all lengths, since a formula has fixed arity. Under per-symbol coding none defines truth for sentences longer than itself, by F1. Between the two, truth is definable fragment by fragment, from just above and never from within.T
Rem. 5.19; F1, G5
master: 00:Z9
G7p25034Decomposition: each classical limitation (Gödel I and II, Tarski, speed-up) splits into a counting and a complexity face. The counting face is a theorem (E2, G1, D1, G6), and $\Con{H}(\D)$ is true at grade (ii). The complexity face is imported (G3), with one reversal (G5). The diagonal is unavailable: per-symbol at every scale (F2), any coding beyond $t(\M)$ (F6).T
python source
Thm. 5.20; D1, E2, F2, F4, F6, F8, G1, G3, G5, G6, G8
master: 00:Z1, 00:Z9
G8p25051Truth in the window: at the scale of F8 no formula $T(v)$ of at most $704\,169$ symbols without variables of $u$ defines truth for the densely coded sentences of length at most $Dk$. Take $\theta=\neg T$ in F8. The names of all $k$ variables take $225\,220$ symbols, so the bound is not one of arity.T
python source
Cor. 5.11; F8
master: 00:Z9
H. Co-extensiveness
H1p25035The effectivity clause: among consistent, effectively axiomatised theories, interpreting $\mathsf{Q}$ forces incompleteness. $\Th(\N)$ is complete at grade (i) only, presentable by nothing. Presburger arithmetic separates unbounded iteration from coding power: it is complete and decidable. Incompleteness tracks an effective description confronting a domain that codes its own syntax.D
Section 6; A1, A2
H2p25036Finiteness, the finite direction: for finite $\M$ the full second-order theory $\ThSO(\M)$ is decidable. A second-order quantifier over $k$-ary relations ranges over the $2^{m^{k}}$ subsets of $\M^{k}$, and exhaustive evaluation decides every second-order sentence.T
python sourceLean, Mathlib
Thm. 6.1
H3p25037Finiteness, the classical direction: if $\M$ contains a countably infinite subset, $\ThSO(\M)$ under full semantics is undecidable. A decision procedure would decide second-order arithmetic truth through a copy of $\N$ (A2). The passage evaluates the infinite ontology by that ontology’s own semantics.T
Thm. 6.1; A2
H4p25038Determinacy meets effectivity only on the finite. The structures whose entire theory, second-order included under full semantics, is decidable are exactly the finite ones, in H3’s sense of infinite (H2, H3). Infinite structures offer determinacy at grade (i) or effectivity over a fragment. Finitude delivers both, at grade (ii).T
Cor. 6.2; H2, H3
H5p25039Trichotomy: consistent, effectively axiomatised theories fall into three disjoint, exhaustive cells. (i) Essentially undecidable theories, whose incompleteness is irreparable. (ii) Theories outside (i) with no finite model, whose incompleteness an effective extension removes. “At least $n$ elements, for every $n$” with a free predicate is one. (iii) Theories with a finite model. Irreparable incompleteness tracks effective self-representation, not cardinality.T
python source
Cor. 6.3; A1, A2
J. Neutrality
J1p25040Evidential force: a certificate’s categorical and conditional content. The categorical content is its end sentence as warranted by the checked steps alone, present exactly when every rule used is locally sound. The conditional content is the end sentence under the undischarged hypothesis that the rules are sound in the inhabited structure. Counterparts agree in both, up to the hypothesis named.D
Def. 7.1
J2p25041Neutrality, certificate level: place a bounded agent in an infinite world under a consistent, effective $\mathsf{Q}$-interpreting description, or in a sufficiently large finite structure. Categorical contents are realised certificate for certificate (D4), and conditional contents transfer verbatim. No certificate available to a bounded agent discriminates the two situations.T
Thm. 7.2; D4, G7
J3p25042The diagnosis: the effectivity hypothesis is the agent, abstracted. The excess of truth over certificates is information about the certifier’s finitude, not about the cardinality of the world. Consequences are drawn for Hilbert’s programme, for the anti-mechanist argument and for the platonist moral. The row is a reading argued from J2.D
Section 7; J2
J4p25043The residue for the finitist: agents get no completeness (E2). No certificate of a part has the totality’s cardinality as its categorical content (D4). Universal arithmetic claims are read schematically, instance by instance below the bound. In exchange, determinacy is effectively realised in full on this ontology alone (H4).D
Section 7; E2, D4, H4
J5p25044Objections O1–O8 are answered. Grade (ii) asserts a specification and a computed size, not the realisation of the evaluation object (O8). The agent bounds are parameters, not psychology (O4). No feasibility predicate is used, and no number is called too large to exist (O5).D
Section 8

Status

I
Import. A standard result, or a corpus result, used without reproof.
D
Definition. A naming, a declared convention or a reading, carrying no claim of its own.
T
Theorem. Derived in the paper, and machine-verified in exact arithmetic where the source column names a witness.

Sources

python source
Gold: the python check that decides the predicate, at its line in the script (the source, rendered on this site); on hover the deciding family and the families that corroborate it, and the verdict of the last run (red when it fails). The script page's bar runs the predicate's cell of the package's notebook on Google Colab (one cell per predicate; the whole notebook from the header badge).
Lean, the coreLean, Mathlib
The predicate as one Lean declaration, named by its accession key (p25010) — the conjunction of the theorems that prove it — at its line in the rendered module, one mark per library that proves it, the core's first. Green: the core (lean/FrcCore) — the statement on the shell ring, by computation and induction, no Mathlib, no axioms: the finitist witness. Violet: Mathlib (lean/FrcLedger) — the classical statement for every shell on Mathlib's hierarchy (its axioms, propext, Classical.choice, Quot.sound, on hover). Red: a proof the gate rejects (an unfinished proof, native_decide) — not a witness. A predicate proved in both libraries shows both marks; one mark, one proof. The module page's bar opens the module as one executable file in Lean Live (the core on plain Lean, no Mathlib; the file elaborates in the browser and prints every predicate's axioms at its end); the header's two Lean badges count the marks of each colour and open the two executables.
section
The statement in the paper's body that carries the predicate: a proposition, a remark or a section.
rests on
The predicates it rests on, by label: realisations, definitions and imports of this ledger, predicates of other ledgers (32:B3) and of the master (00:D15).
What the reader must grant. Five rows are imports: the classical theorems (A1), the model theory (A2), the proof-complexity status (A3, G3) and the corpus results (A4). Fourteen rows are declarations: the setting, the agent and the grades (B1–B5), the scope remarks (C4, D2, E3, F5), the effectivity clause (H1) and the reading of Sections 7–8 (J1, J3–J5). Twenty-nine rows are theorems. The package decides twenty of them on the instances its checks name: C1, C2, C5, D1, D3, E1, E2, E4, F1–F4, F6–F8, G1, G2, G4, G8, H2. For F4 and F6 the checks decide ranges of structures and the base cases of $t(\M)<m$. Lemma 5.8 states the name count for every $k_{1}$ and the bounds of F6. For every structure these bounds rest on the proofs stated with the checks; the body states them without proof. For F7 the checks decide the written formulas on small prime fields, and Lemma 5.9 proves them for every prime. For F8 and G8 they build $\delta$ and $\lambda$ as strings and decide a $\mathrm{Diag}$ of the same construction, at small parameters, on a field of $257$ elements. No check evaluates a formula in a field of the instance: there the fixed point rests on the proof of Theorem 5.10 and on the proofs stated with the checks. The package checks a part of four more rows. For D4 it checks that a record and its end sentence transport to the structure on the cited elements. The proviso and the conclusion on readings rest on the proof. For G5 it checks the label layers of a small coded language and their composition with the pairing prefix. The formula $\mathrm{Truth}_{n}$ and its length bound rest on the proof. For G7 it checks bounded consistency on a small system and two counting cells of the table. For H5 it checks the finite parts of the example in cell (ii). Eleven rows have declarations in the core with no axioms (C1, C5, D1, D4, E1, E2, F1–F4, G4) and nine on Mathlib (C1, C2, C5, D1, D3, E1, E2, F4, H2). Lean proves the whole of rows D3 and G4. For the other rows it proves the combinatorial step of the row. That step is the pigeonhole for C1, C5 and D1. For D4 it is the transport of a term’s value along its cited table entries. For E1 it is the value of every term with the Catalan and cohort counts. For E2 and H2 it is the count. For F4 it is the count of the coding and, in the core, the digit bound $n<dk$. For F1–F3 it is the mention cost over the signature of $\M_p$, with the block length and the split scales of F2. For C2 it is completeness, which holds of every structure, and the decision procedure for a finite one. The interpretation of $\mathsf{Q}$, the syntax of certificates and of codings, the term-to-tree identification of E1 and the asymptotic forms rest on the body’s proofs. Five rows are consequences of the rows they cite: C3, G6, H3, H4, J2. Seven rows evaluate the infinite ontology by its own semantics, as an elimination argument must: A2, F5, H1, H3, H4, the cell boundaries of H5 and situation (a) of J2. No row is open. No row is a realisation, since the paper identifies no physical term. The title claim is G7 with F2, F4 and F6. Below $t(\M)$ the window holds the instance of F8 and the bound of G8, in prime fields of at least $1026$ digits in base $32$. The evidential use of the title claim is J2.