Formal Divergence of Structural Classes

This paper introduces a system-level admissibility criterion to formally distinguish structural classes within the Modal–Dependence Calculus (MDC). The analysis establishes that admissibility is invariant under changes in breadth and depends solely on the universal definability of the dependence relation D*(x, c) across the domain. By comparing closed and open structures, the paper demonstrates that structural divergence is determined exclusively by termination properties, not by size, dimensionality, or expansion. Two structures may exhibit equivalent breadth yet remain formally inequivalent if their admissibility states differ. The result provides a minimal, system-level criterion for structural classification and reinforces the role of closure and termination as necessary conditions for admissibility within MDC.