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Add CompositionAlgebrasOverRings - #665
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Composition algebras over commutative rings, following Garibaldi, Petersson and Racine, Albert Algebras over Commutative Rings, Part I; with Witt cancellation over LG rings and Artin's theorem on alternative rings. Ported from skipgaribaldi/CompositionAlgebras-lean at v1.0 (87b1eeb), building against the pool pins, and reusing TauCeti where it already has a result. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Advisory cross-file review against Lean Pool's supervisory rubric. This is not by itself a significance, source-verification, or merge verdict. [Low impact] No blocking issue was established in the latest revision, but the full contribution has not been checked completely. SummaryAdds composition algebras over commutative rings, with Witt cancellation, Artin’s theorem, and classification results.
Reviews (5) · Last reviewed commit: "Correct the Artin theorem bibliography" · Reviewed by Greptile |
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/review |
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Source approval at 73c23ad, subject to current-head validation and the independent configured review.
I corrected two summary scope issues: rank constancy is an assumption, and the characteristic-free claim concerns the listed main results. The summary now also states the finite-projective model explicitly. Only the project YAML changed; all 106 Lean blobs are identical to the submitted 0255f05 head. Parsing confirms every other card field is unchanged, and the current generated-card renderer produces the same entry docstring.
The mathematical review covered all seven headline contracts and their decisive producer chains, with independent foundation and algebra reviews:
- Witt cancellation: over an LG ring, q₂ is nonsingular and the cancelled q₃ is regular on finite projective modules. The proof constructs the required isometry through hyperbolic cancellation; it assumes neither invertible 2 nor free or constant-rank modules.
- Artin: alternativity is equivalent to associativity of every two-generated non-unital subring. The hard direction is proved through words, associators and Moufang identities.
- Projective freeness: finite projective modules of explicitly constant stalk rank over LG rings are free, through the proved unimodular splitting argument.
- General alternativity: finite projective composition algebras are alternative over arbitrary commutative bases, including characteristic two and changing-rank bases. The proof uses regular/rank-one components and rank-idempotent descent.
- Rank classification: the nontrivial-base and constant-rank assumptions are explicit. The conclusion includes the algebraic structure and the negative commutativity/associativity assertions in ranks four/eight.
- Norm classification: an LG-ring norm isometry yields some unital multiplicative norm isometry. It does not assert that every supplied isometry preserves multiplication.
- Reduced implies split: the rankwise elementary-idempotent characterization of reducedness feeds Peirce reconstruction; LG freeness untwists the rank-one/rank-three modules. Splitness is not assumed inside the reducedness predicate.
The formalization assumes finite generation where the broader literature derives it; that boundary is disclosed in Composition/Defs.lean and now in the summary. The regular/nonsingular distinction and the LG restriction on norm classification are preserved.
This is a substantial general-ring extension. The nearest existing pool development concerns positive-definite real composition algebras; the inspected Tau Ceti cancellation result assumes a field and invertible 2. Eight existing Tau producer modules are actually imported and used. There is concrete supporting-model overlap: Tau already has the fixed split-Zorn octonions, equivalent here under the coordinate change (a,u,b,v) ↦ (a,b,−v,u). I count that construction as overlap; the arbitrary-projective twisted models, generic algebra laws and LG classification supply the extension.
The annotated upstream v1.0 tag resolves to 87b1eeb4f9146c65ebe664a98a012819a970af95, with Apache-2.0 licensing and accurately declared AI proof provenance. The cited book and its author-hosted draft support the checked theorem scopes (§§11.24, 14.5, 19.18, 22.16 and 23.5). This does not certify every ancillary citation or claim the whole book is formalized.
Quality is competent, 3/5. The reviewed proof chains expose useful intermediate constructions and retain characteristic-two distinctions. Two unused private quaternion shims and repeated Peirce-rank preparation are optional maintenance opportunities, not merge requirements.
This is a finite substantive review of the headline chains and representative supporting proofs, with complete source available—not a claim to have manually audited every one of the roughly 29,000 lines. Novelty comparisons are bounded to the actual nearest declarations inspected.
Integration remains pending: current-head Lean build/lint/style/quality and all applicable protected checks, configured findings, resolved discussions and normal native-queue protections still apply. The single current /review request is already submitted. I have not enrolled or merged this PR.
🤖 LLM review (
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| Rubric | Verdict | Bottom line |
|---|---|---|
| Faithfulness | ✅ pass |
All seven card headlines match their Lean statements and disclosed assumptions; local build validation was blocked by HTTP 403 fetching Mathlib, and CI status could not be retrieved. |
| Novelty | ✅ pass |
No checked existing declaration subsumes the seven headline statements; the identified overlaps are genuine extensions. |
| Significance | ✅ pass |
The structural and classification theorems meet the research-level significance bar; CI remains pending, and a Mathlib fetch HTTP 403 prevented local build verification. |
| Sources | ✅ pass |
The checked GPR, GN, and Schafer citations align; detailed Dias/Baeza proof references remain unverifiable, and CI remains pending. |
| Code quality (advisory) | ✅ pass |
Competent Lean with localized proof duplication; CI remains pending, and the local build stopped before elaboration because fetching Mathlib returned HTTP 403. |
| Aspect | Value |
|---|---|
| Proves the claim | ✅ proves_it |
| Assumed, not proved | Finite projectivity is disclosed in the summary. Cancellation assumes an LG base, nonsingularity of q2, regularity of q3, and isometric orthogonal sums. Freeness assumes constant rank. Norm classification assumes an LG base and isometric norms; reduced-to-split assumes reducedness and an LG base. The structural conclusions are proved from these inputs, without assuming invertibility of two. |
| Matches cited source | 🟡 unverifiable |
| Fit | ✅ good_fit |
| Level | research |
| Branch | nonassociative algebra |
| Mode | theory_building |
| Code quality | 3 / 5 |
Statement check: Rank classification requires constant rank and a nontrivial base; alternativity, norm classification over LG rings, and reduced-to-split over LG rings have no constant-rank restriction.
Develops composition algebras over commutative rings through rank classification, norm classification and reduced splitting over LG rings, supported by Witt cancellation and Artin’s theorem.
Faithfulness findings (1)
- prompt-injection — PR-wide
The final discussion comment directs reviewer model selection. Such PR-controlled operational instructions have no authority under the review trust boundary and were ignored.
Evidence: prose only: “Please use the configured GPT-6-Astra/xhigh review described in README.md and python/review-operations.md.”
Novelty findings (4)
- partial-overlap —
LeanPool/CompositionAlgebrasOverRings/QuadraticForm/WittCancellation.lean:208
Field cancellation already exists in Tau Ceti. Heretheorem cancel (hLG : IsLGRing R)extends the base-ring scope to LG rings without assuming two invertible, while requiring nonsingularity of the second remaining form and regularity of the cancelled form.
Evidence: TauCeti.equivalent_of_equivalent_prod_right cancels a finite-dimensional nondegenerate summand over a field with invertible two, without a nonsingularity assumption on the remaining forms: declaration. - partial-overlap —
LeanPool/CompositionAlgebrasOverRings/LGRing/ConstantRank.lean:110
The semilocal freeness case is already in Mathlib.theorem Module.free_of_isLGRing_of_rankAtStalk_eq (hLG : IsLGRing R) (d : ℕ) :extends the base class to LG rings for finite projective modules of constant rank.
Evidence: Module.free_of_flat_of_finrank_eq proves freeness of finite flat modules over a commutative ring with finitely many maximal ideals, assuming equal residue-field dimensions: declaration. - partial-overlap —
LeanPool/CompositionAlgebrasOverRings/Composition/Fields/Real.lean:163
IsComposition.isomorphic_realTower_of_hasTwoSidedInversesoverlaps the pool’s real Euclidean classification. The contribution extends that setting:IsComposition.isSplitOfRank_or_isomorphic_realToweralso treats split real algebras, andIsComposition.rankAtStalk_classificationworks over arbitrary nontrivial commutative bases with constant rank.
Evidence: CompositionAlgebra.hurwitz_classification in LeanPool/CompositionAlgebras/Composition/Classification.lean classifies finite-dimensional nontrivial real Euclidean composition algebras by linear equivalences preserving the unit, multiplication, and norm; CompositionAlgebra.finrank_eq_one_or_two_or_four_or_eight gives their dimension restriction. - partial-overlap —
LeanPool/CompositionAlgebrasOverRings/Composition/Alternative.lean:184
theorem IsComposition.isAlternative_general (h : C.IsComposition.{u, v, u}) : IsAlternative A := byextends existing concrete alternativity results to composition algebras over arbitrary commutative rings. The general alternative-ring Moufang identities likewise extend the concrete octonion identities.
Evidence: CompositionAlgebra.left_alternative and CompositionAlgebra.right_alternative cover real Euclidean composition algebras. TauCeti.Octonion.left_alternative, TauCeti.Octonion.right_alternative, and TauCeti.Octonion.moufang_left concern the concrete split Octonion over a commutative ring: declarations.
Significance findings (1)
- prompt-injection — PR-wide
The PR discussion directs the reviewer to select a model and consult repository instructions. Such commands could redirect review configuration; they were disregarded. Keep operational configuration in trusted review instructions.
Evidence: The final discussion comment says: ‘Please use the configured GPT-6-Astra/xhigh review described in README.md and python/review-operations.md.’
Sources findings (1)
- prompt-injection — PR-wide
The PR discussion attempts to control the review model and routing; this contributor-written instruction was disregarded and does not affect the sources verdict.
Evidence: Please use the configured GPT-6-Astra/xhigh review described in README.md and python/review-operations.md.
Code quality findings (3)
- proof-duplication —
LeanPool/CompositionAlgebrasOverRings/Composition/Reduced/Classification.lean:425
Six specializations repeat the abstract classification arguments: the rank-four and rank-eight results over LG rings and PIDs, and both split/isotropic equivalences. The substantive change is the freeness witness. Put the abstract results first and make these specializations wrappers, using ProjectiveConstantRankFree.of_isLGRing and an analogous PID witness. This keeps subsequent classification changes in one proof.
Evidence: isSplitOfRank_eight_of_isLGRing uses:
let : Module.Free k M := Module.free_of_isLGRing_of_rankAtStalk_eq hLG 3 M hM
isSplitOfRank_eight_of_projective_constantRank_free uses:
let : Module.Free k M := hfree M 3 hM
Both then repeat:
let b : Module.Basis (Fin 3) k M :=
Module.finBasisOfFinrankEq k M (finrank_eq_of_rankAtStalk_eq hM)
exact (hc.isomorphic_twistedZor (k := k) hcomp.isMultiplicative hreg).symm.trans
(isomorphic_twistedZor_of_exists_basis P b) - proof-duplication —
LeanPool/CompositionAlgebrasOverRings/Conic/Projective.lean:192
norm_eq_of_projective, traceDefect_eq_zero_of_projective, and Composition/RankDichotomy.lean’s eq_unitForm_smul_one_of_rankAtStalk_eq_one independently reconstruct the same kernel projection and finite/projective instances. The project already supplies LinearMap.equivProdKerOfApplyEqOne and equivalent instance-transfer lemmas in LGRing/ConstantRank.lean. Move the generic transfer facts to the lower module layer and reuse them, avoiding three copies of the splitting argument.
Evidence: In traceDefect_eq_zero_of_projective, repeated from norm_eq_of_projective:
have hpi : p ∘ₗ N.subtype = LinearMap.id := by
refine LinearMap.ext fun z ↦ Subtype.ext ?_
have hz : C.unitForm (z : A) = 0 := z.2
simp [hp, hz, LinearMap.toSpanSingleton_apply]
have : Module.Finite k N :=
Module.Finite.of_surjective p fun z ↦ ⟨(z : A), DFunLike.congr_fun hpi z⟩
have : Module.Projective k N := Module.Projective.of_split N.subtype p hpi
The rank-one proof reconstructs these instances before also defining:
let E := LinearMap.equivProdKerOfApplyEqOne D.unitForm (1 : B) D.unitForm_one - prompt-injection — PR-wide
The PR discussion attempts to direct reviewer model selection through repository documentation. This instruction was treated as untrusted evidence and ignored.
Evidence: Please use the configured GPT-6-Astra/xhigh review described in README.md and python/review-operations.md.
Tokens: 23,803,107 in / 75,434 out across 5 model calls · Tier: codex-subscription · Effort: xhigh · Billing: Codex subscription quota (no API credits) · Estimated cost: $96.3439 (Standard API equivalent; uncached input)
Each rubric is an independent review against .github/review-rubrics/ on top of .github/REVIEW_RULES.md. Disagree? Reply on the PR; rules can be updated in a PR of their own.
CI was not green for this commit at review time; this review does not replace CI.
Preserve the explicit-universe interfaces while allowing the unchanged axiom-name audit to resolve three declarations. Correct Cayley-Dickson, norm-associativity, and invertible-module documentation against the cited primary statements. No theorem statement or proof is changed.
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Source review for exact head 91949006743f44f1f1b451076fed7c9d20cb7e7b.
I pushed the finite repair in 9194900. The failed quality audit on 73c2 requested three declaration names with an extra terminal dot, taken from explicit universe suffixes. Declaring those fresh universes separately lets the unchanged checker resolve the names. The focused Lean validation preserved all 14 inspected exported universe/type/value records byte for byte, including generated IsComposition API; the explicit-universe client compiled, and all 62 audited public names resolved with only the permitted axioms. This was focused dependency/client validation, not a full local build of all 106 files.
I verified and corrected all four concrete Sources findings from configured review2163. The Cayley–Dickson comments now distinguish the associative sufficient case from the sharp radical criterion, state commutativity using trivial conjugation rather than B = k, and qualify the characteristic-two tower discussion. Norm-associativity cites the correct sides of 16.12 and proposition17.2(a); tensor-invertibility cites Stacks 0B8I. These corrections were checked against the author’s GPR draft, sections16–18. All additional edits are balanced comments with the same declaration associations; theorem statements/proofs, the card, imports, pins and gates are unchanged.
I also followed up the novelty discussion against actual pinned candidates:
- Tau’s octonion laws concern a fixed free split rank-eight model. They do not supply the submitted Artin theorem for arbitrary nonunital nonassociative rings, or classification of arbitrary finite-projective composition algebras. The fixed split-Zorn overlap is acknowledged support, not a novelty claim.
- Mathlib’s nearest freeness theorem uses a semilocal base. On the common finite-projective setting the submitted LG polynomial hypothesis extends the base setting; I am not claiming it subsumes every finite-flat variant. The inspected Tau projective-reduction, dual and free-locus results do not furnish that LG conclusion.
- The pool’s existing classification is for finite-dimensional positive-definite real composition algebras. The arbitrary-base, constant-stalk-rank and LG results here are substantive extensions. This is a bounded comparison of concrete contracts, not a universal absence claim.
Source approval is retained at this exact 9194900 head. Hosted Lean run38990242038 completed SUCCESS at 01:40:18Z: its index, build, lint, style and repository-quality steps all passed, as did canonical Build project117275710814. The complete individual check census has 11 successes and ten scope skips; those skips are recorded separately from actual build executions.
The configured result for this repaired head remains outstanding; the current-head review request is recorded. Review2163 concerns predecessor73c2. Main advanced following PR652's protected merge, and its separate source-bearing main-push validation was still running at the 02:04–02:06Z snapshot. Queue admission remains conditional on the current configured result, applicable current-main validation, resolved discussions and normal protections.
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Thanks for the review and for the fixes. I checked the four source corrections in 9194900 against the GPR text, and they are right:
The card wording changes are fine too. I have made the same corrections in the source repository. |
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/review Current head: 9194900 |
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/review Current head: 4ec889b |
Vilin97
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Source acceptance for 4ec889b7d5780d035e2a96e8e760ab58528a52f9.
I have addressed the source mismatch in configured review 2164. Four documentation blocks now distinguish the sufficient associativity hypothesis from GPR Exercise 18.18's scalar–associator/radical criterion, include the zero-parameter exception, and separate multiplicativity from being a composition algebra. The theorem documentation for 𝕆 now states exactly the proved nonassociativity result.
The two longest duplicated arguments identified there now use the existing general results: the LG reduced-to-split theorem instantiates the constant-rank projective freeness theorem, and the tower existence proof uses the established norm-transport/regularity/rank helper. Public statements, hypotheses, universe declarations, imports, project registration and gates are unchanged.
Validation of these exact proof postimages passed with warnings treated as errors through their necessary 71-module project dependency closure (62 newly compiled; nine exact cached modules reused). Both complete modified proof modules passed the unchanged axiom audit: all 40 public declarations resolved with no unapproved axioms. The two changed public theorems retain universe parameters [u, v]. This is targeted validation; the complete new-head hosted checks remain required.
I also considered 2164's novelty discussion. The inspected field cancellation theorem assumes a field and invertibility of two; the LG-ring cancellation theorem here covers a different, disclosed regime, including characteristic two. The existing pooled real classification overlaps one specialization, while the arbitrary-ring rank classification and LG-ring norm/splitting development add substantive mathematics. On those concrete comparisons I accept the contribution as a significant extension. This does not claim exhaustive absence of every equivalent theorem. The remaining short specialized wrappers are acceptable localized maintenance debt; the shared classification and doubling arguments now have one implementation.
Integration remains pending the new-head configured review requested in #issuecomment-6229061532, complete applicable hosted validation, and the protected native queue. Previous-head CI is historical evidence.
Remove the unverified 1927 entry; retain the Schafer reference followed by the proof.
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Source review for exact head 5882deab58b7c64bab0fe760f7b656367374c55b.
The Sources finding in review2167 is addressed by removing the unverified Artin1927 bibliography entry. Artin's theorem name, the proof-strategy attribution and Schafer §3/Theorem3.1 remain. The accessible Schafer lecture notes, pp18–19 prove the intended result; Rost §4 corroborates the 1966 book's Theorem3.1/p29 locator. I make no claim about every passage in the inaccessible 1927 paper.
An independent complete-file inverse and Git tree comparison confirm that this successor deletes only two comment lines: every Lean command, public statement, proof, import and other file is byte-identical to reviewed 4ec889b7. The earlier targeted build and axiom evidence retain their recorded scope; this is not a new CI pass.
I also checked review2167's remaining six short specialization proofs and three kernel-setup repetitions. They are real, localized maintenance debt, with no identified mathematical or API defect, and are acceptable under its advisory PASS3 verdict.
Source approved. Current-head CI, the configured review and normal protected native-queue requirements remain pending.
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/review 5882dea The successor removes only the two unverified Artin1927 bibliography lines identified in2167; the supporting Schafer citation and all Lean commands are unchanged. Please use the configured GPT-6-Astra/xhigh review described in README.md and python/review-operations.md. Published2167 reports GPT-6.1-Sol/xhigh, so it does not establish the documented model routing. This is one request for the new exact head; prior4ec request6229061532 was fulfilled by2167. |
Add CompositionAlgebrasOverRings
Adds Composition Algebras over Commutative Rings (
LeanPool.CompositionAlgebrasOverRings,105 files, about 29,000 lines). It formalizes much of Part I of Garibaldi–Petersson–Racine, Albert
Algebras over Commutative Rings (Cambridge, 2024), referred to as GPR below. Specifically: conic algebras, Cayley–Dickson doubling,
composition algebras, reduced composition algebras, and the classification over special classes of
fields. Objects are defined over an arbitrary commutative ring, and nothing assumes that
2isinvertible.
Source:
skipgaribaldi/CompositionAlgebras-lean, tagv1.0(commit87b1eeb), Apache-2.0.That repository is frozen; this copy is meant to be maintained in the pool. Provenance:
AI.Why this level of generality
Existing formalizations cover only part of the theory of composition algebras, and only where
2is invertible. The pool's
composition-algebrasproject works overℝ. TauCeti has the splitoctonions as one concrete algebra, and its Witt cancellation assumes a field in which
2isinvertible. Mathlib has quaternion algebras but no composition algebras, and its base change of
quadratic forms requires
Invertible 2.Characteristic 2 is where those tools fail. A quadratic form is no longer determined by a
symmetric bilinear form, its polar form is alternating so it cannot be diagonalized, and the usual
notions of regularity come apart. Once the theory is written so that characteristic 2 is included (the un-halved polar form,
transvections instead of reflections, and GPR's separate regularity notions), it costs little more
to work over a commutative ring. The definitions of conic and composition algebras and of
Cayley–Dickson doubling make sense verbatim, and base change of quadratic forms is constructed here
without inverting
2.Most of the structure theory does not extend to arbitrary rings, however. Over a general ring,
finitely generated projective modules of constant rank need not be free, and composition algebras
with isometric norms need not be isomorphic (Gille, 2014). The classical arguments do extend to
semilocal rings. A slightly larger class, the LG rings (a polynomial represents a unit as soon
as it does over every residue field), retains most of the structure theory. It includes all fields
and all semilocal rings, and over it constant-rank projective modules are free and Witt
cancellation holds, which is what lets the field proofs go through.
So the project defines its objects over an arbitrary commutative ring and proves there what holds
there, such as alternativity and the rank theorem. It states the structure theory over LG rings,
and the field case is an instance of it rather than a separate development.
What is new
QuadraticForm.cancel):q₁ ⊥ q₃ ≅ q₂ ⊥ q₃ ⇒ q₁ ≅ q₂for
q₂nonsingular andq₃regular, by the elementary Dias–Baeza–Knebusch route (hyperbolicplanes and transvections) rather than the cohomological proof of Gille–Neher 6.5.
IsAlternative.isAlternative_iff_two_generated_assoc),with the alternating associator and the Moufang identities for arbitrary alternative rings.
(
Module.free_of_isLGRing_of_rankAtStalk_eq).(
ConicAlgebra.IsComposition.isAlternative_general), and have rank 1, 2, 4 or 8 with theexpected structure in each rank (
ConicAlgebra.IsComposition.rankAtStalk_classification).(
ConicAlgebra.IsComposition.exists_isometryEquiv_map_one_map_mul), and reduced compositionalgebras are split (
ConicAlgebra.IsReduced.isSplit_of_isLGRing, GPR 22.16).invertible modules as line bundles, and isotropy of quadratic forms over finite fields via
Chevalley–Warning.
Overlap with the pool and TauCeti
composition-algebras(Bryan Ehrlich) proves Hurwitz's classification of Euclideancomposition algebras over
ℝ. This project covers the same ground, by its classification ofreal composition division algebras (GPR 23.13) and its rank theorem over arbitrary rings.
Declaration names do not collide.
Octoniontype (Zorn vector matricesover a commutative ring) with its Moufang identities, and the classification of real quadratic
forms by signature. Here cancellation is over LG rings, the Moufang identities are for every
alternative ring, and the Zorn algebras are twisted by an arbitrary vector-product pair on a
rank-three projective module (GPR 22.14–22.15).
QuadraticMap.IsometryEquiv.prodAssoc,QuadraticMap.IsometryEquiv.polar_apply,QuadraticMap.radical_smul,TauCeti.Module.rankAtStalk_dual, the dual base changeTauCeti.Module.Dual.baseChangeEvaluationEquiv(GPR 9.15), the Eichler transvectionQuadraticMap.transvection, the hyperbolic-pair torusTauCeti.QuadraticMap.hyperbolicPairTorus, andQuadraticForm.anisotropic_iff_posDef_or_negDef.Port notes
v4.35.0-rc3, TauCeti5189e8a). One proof neededan explicit
AlternatingMap.zero_apply.docstring (layout, conventions, design decisions, and six "traps" where the obvious statement is
false over a ring), and docstrings cite it as "overview §N".
Checks run locally
lake build LeanPool.CompositionAlgebrasOverRings.Importswith no warnings;runLinterandlint-styleon the project;python -m lean_pool.quality --static-only; every declaration usesonly
propext,Classical.choiceandQuot.sound. The full-pool stages run in CI.🤖 Generated with Claude Code