**Motivations:**
- Make Lemma C2 assertions citeable without terminal transcripts
- Provide a deterministic check for “both-children residual” and projective projection to B12
**Root causes:**
- C2 relied on narrative links between completion docs and B12 invariance without a machine-checkable artefact
**Correctifs:**
- Add a deterministic verifier that checks set equalities and projections from the existing completion MD sources
**Evolutions:**
- Version C2 verification artefacts in docs/artefacts
- Add a run report profile (sha256 + metrics) for C2 projective verification
- Update the proof plan with explicit C2 statements and references
**Pages affectées:**
- applications/collatz/collatz_k_scripts/collatz_verify_c2_projective.py
- docs/artefacts/collatz/c2_projective/verification_c2_projective.json
- docs/artefacts/collatz/c2_projective/verification_c2_projective.md
- applications/collatz/collatz_k_scripts/collatz_generate_run_report.py
- docs/collatz_run_report_2026-03-09_c2_projective.md
- docs/collatz_run_report_format.md
- docs/features/collatz_run_report_generator.md
- docs/features/collatz_c2_projective_verification.md
- applications/collatz/collatz_k_scripts/plan_lemmes_manquants_et_programme_de_preuve.md
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