Reduction of Datum-Neutrality to Discrete Motion and Shared Datum in the Compact Fiber

Reduction of Datum-Neutrality to Discrete Motion and Shared Datum in the Compact Fiber This note proves that the datum-neutrality principle P5′, used in the companion paper The Compact Fiber as the Canonical Admissibility Structure for Discrete Scalar Motion (Paper I; DOI: 10.5281/zenodo.19423877), is reducible to the base postulates P1 (discreteness) and P5 (shared datum) within the A5 closure setting. Paper I derives the compact fiber F ≅ Z₄ × Z₄ × Z₈ from postulates P1–P5, axiom A5, and a datum-neutrality condition P5′, with Results 1–6 unconditional and Results 7–11 conditional on P5′. Paper I explicitly left open whether P5′ is an irreducible additional principle or a consequence of the base postulates. This note resolves the question. The argument factors into two independently motivated lemmas: Admissibility maximality (from P1): Intrinsic closure invariants generated by primitive motion are part of the admissibility data unless eliminated by a valid equivalence. Datum zeroing (from P5): The shared datum zeros all admissibility data. Their conjunction yields P5′. No new algebraic result is required beyond what Paper I already proves; the note invokes Paper I's intrinsic-orientation proposition (Prop 5.7), nontrivial-residue proposition (Prop 8.4), and non-reducibility proposition (Prop 8.8). As a corollary, the conditional flag on Paper I Results 7–11 is discharged. The full compact fiber Z₄ × Z₄ × Z₈ is forced from P1–P5 and A5 alone. No independent datum-neutrality principle is required. This note does not modify the algebraic construction of Paper I; it changes only the dependency status of P5′.