The crux layer — the statement whose HAND proof once carried the frontier
coverage bug is now kernel-checked.
- gen: hash outputs refactored to Hash = {l : List UInt8 // l.length = 32}.
MECHANIZATION FINDING: the paper's pair-coincidence step ('equal hnode
values of distinct argument pairs are a collision') is load-bearing on
FIXED-WIDTH outputs — with unconstrained byte strings x++s = X++Y does
not split. hnode_preimage_inj (cone: propext) makes this explicit via
List.append_inj on equal-length components. Queued as a half-sentence
for the paper's next cycle.
- HasCollision := ∃ x y, x ≠ y ∧ sha256 x = sha256 y — appears ONLY as a
conclusion, never a hypothesis (no collision-resistance assumed).
- hnode_inj_or_collision / hleaf_inj_or_collision: the per-node dichotomy.
- root_binding: any accepting reconstruction from (v,P) to the honest root
either IS the honest receipt (leaf hash AND full path P = Path m D — case
(ii) pinning every consumed sibling) or exhibits a collision. Motive
quantifies (v,P); induction on Path; k-fold discipline.
- incl_sound (Theorem 2, position binding): accepting a wrong leaf at m
yields a collision. Cone [propext, Classical.choice, LTLAcc.sha256,
Quot.sound] — the single hash axiom, pinned in check.sh. ALL GREEN.
Also: Root n=1 branch changed from list-match to decidable 'if P = []'
(well-founded unfolding generated a spurious exhaustiveness obligation);
Root_one_cons added. Fable-5 statement-audit passed. LTL untouched.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Accumulator pyramid layers 1-2, mechanizing paper SS5.3/SS6 groundwork:
- gen/LTLAcc/HashExternal.lean: the single sanctioned axiom, opaque
sha256 (no properties assumed - the soundness theorems downstream are
constructive collision extractors).
- Proofs/Basic.lean: hleaf/hnode (0x00/0x01 domain stamps); Lemma 1
(domsep) proven AXIOM-FREE; kbelow (largest power of two below n)
with pos/lt/le-two bound lemmas; MTH, Root (Option = rejection),
ConsRec (four cases, b-flag, pinned anchor) - all with kernel-checked
termination via the kbelow bounds.
- check.sh: estate discipline (stub audit, axiom-smuggling gate,
lean-guard compilation, boundary-exact per-certificate cone audit).
All green; observed cones pinned exactly.
Zero contact with the live LTL: no appends, no server, accumulator
frozen at 12 leaves throughout this project.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
