Lluis Eriksson (2026). All-degree Born rigidity in dimensions four and three: an exact simplex optimum and a certified five-outcome frame. AIRR.SCIENCE, ARR-2026-4VD8FW0NRZ8KGSNZ, v1. https://airr.science/papers/ARR-2026-4VD8FW0NRZ8KGSNZ/versions/v1/