INV-25 makes the GSM8K lesson structural: no capability claim is valid unless
its gold is computed by a procedure sharing no code with the system under test.
Three meaningfully-failing checks (proven able to fail): 25a oracle imports no
SUT module (AST); 25b every committed deductive gold is reproduced by the
independent oracle AND matched by the engine; 25c an unsound engine disagrees
on committed cases.
SHA-pin the deductive lane (deductive_logic_v1, dev+holdout+external 716/716,
wrong=0, refused=0) via a deterministic --report writer + run_as_module (the
lane dir's local generate.py shadows the package in script mode) + CLAIMS regen.
Fix drift the review surfaced: contract.md + pivot doc claimed an 8,000/7,340
fuzz and an 'external mirror' -> corrected to the real gated 3,000-case fuzz
(2,796 definite) and 'hand-authored, NOT a published-benchmark mirror'; pivot
doc GSM8K holdout 0->5 (all 5 are R1 reconstruction; composer scored 0).
Validated: smoke 78, deductive 23, proof 29, invariants 44, lane-sha+claims 9.
The first SIZEABLE, honestly-verified reasoning capability — built on CORE's
own terrain (exact, verifiable, deterministic), not GSM8K's stochastic terrain.
THE OPERATOR (generate/proof_chain/entail.py, ADR-0206):
- evaluate_entailment(premises, query) -> entailed | refuted | unknown | refused.
- The multi-hop inference operator evals/symbolic_logic/gaps.md said did not exist
("no operator that takes A->B, B->C and returns A->C") and ADR-0205 deferred.
- Built on the ADR-0201 ROBDD canonicalizer: premises |= Q iff (AND P) -> Q is a
tautology. SOUND AND COMPLETE for propositional logic, not single-step.
- wrong=0 is structural: an exact tautology check refuses (LogicError) on
malformed / out-of-decidable-regime (quantified/predicate) input, never guesses.
THE HONEST METRIC (evals/deductive_logic/):
- holdout v1 (500 cases): 500 correct / 0 WRONG, incl. 227 non-trivial deductions
(117 entailed + 110 refuted). dev (200): 200/0.
- Gold from an INDEPENDENT truth-table oracle (oracle.py) sharing zero code with
the engine. 8,000-case fuzz across two independent decision procedures:
0 disagreements. This is the soundness evidence the GSM8K composer could never
produce (it could not separate its 2 right from its 87 wrong answers).
- contract.md states the load-bearing honesty boundary: PROPOSITIONAL ONLY, and
given-formulas (NL->logic grounding is a separate later layer, kept out of scope
so we do not re-step on the GSM8K natural-language rake).
TESTS (17, all green): classic inference shapes (MP, multi-hop chain, modus
tollens, disjunctive/hypothetical syllogism, conjunctive rules, genuine unknown),
refusal boundary (inconsistent / quantified / predicate / malformed), and a
deterministic engine-vs-oracle fuzz cross-check.
Pure new module — does NOT touch serving. Smoke 73 passed; invariants 40 passed.
