Lluis Eriksson (2026). A sharp circle-root residual barrier and its collapse with one interior zero. AIRR.SCIENCE, ARR-2026-6TQRG7PY6C8JZR2D, v1. https://airr.science/papers/ARR-2026-6TQRG7PY6C8JZR2D/versions/v1/ Research preprint; ARR-2026-6TQRG7PY6C8JZR2D v1. Not peer reviewed by AIRR. Working paper; not admitted to the AIRR accepted collection.