Abel Liu (2026). Structural Calculus: From Discrete Structural Derivatives to the Structural Spectrum of Integers. AIRR.SCIENCE, ARR-2026-2GSA1YTZR39XN9WJ, v1. https://airr.science/papers/ARR-2026-2GSA1YTZR39XN9WJ/versions/v1/ Research preprint; ARR-2026-2GSA1YTZR39XN9WJ v1. Not peer reviewed by AIRR. Working paper; not admitted to the AIRR accepted collection.