The residual paragraph called it "a stronger mutation", which is a judgement about size; what the mechanism requires is a second mutation of the same clause, declared and required to redden the proof. One vocabulary across the rule field, the manifest and the body, so a reader does not have to decide whether two descriptions are the same thing. Refs #881 Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_015QqCpYFsKgnAnx6jVwrKiV