KERNEL TRUST PROFILE

a standard way to say what a proof rests on · version 0.1, draft

SPEC.md · JSON Schema · 14 worked profiles below · CC-BY-4.0

Version 0.1 (draft) — 2026-08-05

A machine-readable declaration of what a body of machine-checked mathematics rests on.

0. The gap this fills

A proof assistant reports that a proof checks. It does not report that the theorem is standing on an unfinished proof several files upstream, or that the result was obtained by trusting a compiler rather than a kernel. Both look exactly like success, and neither is visible to anyone downstream.

There is a standard way to say how to cite a project (CITATION.cff), and a standard way to say what licence it carries (SPDX). There is no standard way to say what it rests on. Every project states it in prose, or not at all.

A Kernel Trust Profile is that statement, in a fixed shape, computed from the artifact rather than asserted by its author.

1. Scope

A profile describes one library, at one revision, as measured by one tool at one time. It carries no claim about correctness, quality, or importance, and it is not a certificate. It reports provenance: which trust assumptions the library's theorems actually reach.

Consistency is not in scope and cannot be. A profile scopes the risk; it does not eliminate it.

2. Design rules

These are the rules that keep a profile from becoming a badge.

R1. Mechanically recomputable. Every number MUST be derivable by a third party from the named revision using the named tool. No field may hold a value that only the author could know.

R2. Absence is not zero. A profile MUST distinguish "measured, and the count is zero" from "not measured". null means not measured. Omitting a field means not measured. Writing 0 is a positive claim and MUST be backed by a measurement.

R3. Statement and proof stay separate. Where a dependency is reported, a profile MUST record whether it enters through a theorem's statement or only through its proof. Collapsing the two discards the distinction that makes the measurement actionable: a statement dependency changes what was proved, a proof dependency changes only how.

R4. Reach, not amplification. Reach — the fraction of a library depending on an assumption — is invariant under inlining and factoring. Amplification is not: factoring a shared step into a lemma changes it without changing anything the library proves. A profile MAY report amplification, MUST report reach, and MUST NOT rank libraries by amplification.

R5. No composite scores. A profile MUST NOT contain a single number summarising trustworthiness. A theorem either reaches an unfinished proof or it does not; averaging that against anything else invents precision that the underlying measurement does not have.

R6. Tool-agnostic. A profile MUST be emittable by any tool that can compute the declaration graph. Nothing in this specification requires a particular implementation. A format only one program can produce is a file format, not a standard.

3. Format

A profile is a JSON document, conventionally at the repository root as kernel-trust.json, UTF-8, conforming to the schema in schema/kernel-trust-0.1.schema.json.

{
  "ktp_version": "0.1",
  "generated_at": "2026-08-05",
  "generated_by": { "tool": "gonzalgo", "version": "0.5.2" },
  "subject": {
    "name": "Mathlib",
    "system": "Lean 4",
    "system_version": "4.32.1",
    "revision": "a1b2c3d",
    "foundation": "dependent type theory"
  },
  "counts": {
    "declarations": 790171,
    "theorems": 437429
  },
  "unfinished": {
    "theorems_reaching": 0,
    "axioms": ["sorryAx"]
  },
  "compiler_trusted": {
    "theorems_reaching": 0,
    "axioms": ["Lean.ofReduceBool", "Lean.ofReduceNat"]
  },
  "assumptions": [
    {
      "name": "Classical.choice",
      "kind": "optional",
      "entry_points": 144,
      "reach": { "theorems": 324808, "fraction": 0.6100 },
      "via": "proof"
    },
    {
      "name": "propext",
      "kind": "foundational",
      "entry_points": null,
      "reach": { "theorems": 437429, "fraction": 1.0 },
      "via": "both"
    }
  ]
}

Fields

ktp_version (required) — the version of this specification.

generated_at (required) — ISO 8601 date the measurement was taken.

generated_by (required) — tool and version. Identifies what to re-run.

subject (required) — what was measured. revision SHOULD be a commit hash or released version, so R1 is satisfiable.

counts (required) — theorems is the denominator for every fraction.

unfinished (required) — theorems reaching an unfinished proof from anywhere upstream, and the axiom names that signal it. theorems_reaching: 0 is the claim most worth making and, under R2, the one that must be measured to be stated.

compiler_trusted (required) — theorems reaching a result obtained by trusting the compiler and runtime rather than the kernel.

assumptions (required, may be empty) — one entry per axiom or assumption reached by any theorem.

• kind — foundational (the system's own basis, unremarkable), optional

(removable in principle, e.g. choice), or escape-hatch (unfinished or compiler-trusting).

• entry_points — declarations whose own proof cites it, as opposed to

inheriting it. null where not computed.

• reach — theorems depending on it at all, and that count over counts.theorems.
• via — statement, proof, or both, per R3.

4. What a profile does not mean

A library reaching 61% of its theorems with the axiom of choice has made a design decision, not an error. Metamath's set.mm tiers countable and dependent choice separately on purpose and reaches 1.2%; Lean core does not, and its maintainers have stated that avoiding choice is a deliberate non-goal. Both are coherent. A profile makes the difference legible; it does not adjudicate it.

Under R5 there is no score, so there is no ranking, so a profile cannot be used as a league table without leaving the specification.

5. Versioning

Additive changes increment the minor version. Any change to the meaning of an existing field increments the major version. A consumer encountering an unknown ktp_version major MUST NOT interpret the document.

6. Prior art

CITATION.cff standardises citation metadata; SPDX standardises licence identifiers; codemeta.json standardises software description. Each took a thing every project stated in prose and gave it a shape. This does the same for the trust assumptions under a machine-checked result.

The measurements are defined in Where Formal Libraries Spend Their Axioms, https://doi.org/10.5281/zenodo.21769846, which also gives the refactoring argument behind R4 and the statement/proof separation behind R3.

7. Licence

This specification is CC-BY-4.0. Implementations are unencumbered.

Profiles

Fourteen libraries, emitted by gonzalgo profile from the Kernel Index. These exist to test the specification against data gathered before the specification was written — a format that only fits the numbers you happen to have is not a standard.

The unmeasured column is the specification working. Rule R2 says absence is not zero and null means not measured, so four fields sit null across every profile — system version, revision, url, and the declaration count — because those measurements were never taken. Filling them from a different measurement is what R1 forbids.