Invariant Admissibility Constraints - A Domain-Independent Definition of Law

This preprint proposes a domain-independent definition of law as an invariant admissibility constraint. A law, in the strict sense, is not merely an empirical regularity, formal expression, model, rule, norm, or protocol. It is a constraint that determines what remains admissible within a specified domain and whose status is preserved under admissible transformations of regime. The paper develops a minimal formal vocabulary for distinguishing law from adjacent structures and proposes a practical diagnostic: what disappears with a regime, and what remains admissible after transformation? The framework is intended as a methodological classification tool applicable across philosophy of science, physics, biology, computation, economics, constitutional analysis, institutional systems, and complex systems.