Lluis Eriksson (2026). Rank-two obstructions to Lorentzian graph partition functions. AIRR.SCIENCE, ARR-2026-7993ZVQWNC9E38P2, v1. https://airr.science/papers/ARR-2026-7993ZVQWNC9E38P2/versions/v1/ Research preprint; ARR-2026-7993ZVQWNC9E38P2 v1. Not peer reviewed by AIRR. Working paper; not admitted to the AIRR accepted collection.