Relative PSC and Recursive NEMS (Fractal Closure) Paper 16 (C2) of the NEMS Suite

We introduce the concept of relative closure for subsystems within the No External Model Selection (NEMS) framework. By defining a subsystem as an autonomous framework FA with its own internal model, records, and truth relations, we prove a powerful recursion principle (Recursive NEMS): if a subsystem implements complete internal semantics (BICS) for its own records, it necessarily satisfies NEMS relative to its environment. Furthermore, we prove the heredity of the diagonal barrier: if a subsystem is rich enough to host Arithmetic Self-Reference (ASR), the undecidability of its internal record-truth applies directly to it, rendering its internal adjudication non-emulable by any total-effective algorithm. This establishes the "fractal" nature of semantic closure in NEMS. We also present a strengthened version of the No-Emulation theorem (deferred from Paper 15), explicitly formalizing the instance-level encoding that bridges physical emulation and computational decidability. All definitions and theorems are fully machine-checked in Lean 4. This overview presents the core NEMS theorem engine and selected applications; stronger domain-specific derivation and ontological synthesis claims belong to separate release surfaces with their own premise bundles and formal artifacts. Trust boundary. Recursive NEMS and stronger no-emulation use the subsystem formalism and instance encoding as defined in nems-lean ; "fractal closure" is shorthand for those proved heredity lemmas, not an additional metaphysical posit. See.