FPF Reference

    A.6.P:4.1 — Stable lens

    Preface node heading:a-6-p-4-1-stable-lens:12430

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    A RPR‑pattern SHALL name a stable mathematical “lens” that prevents re‑inventing roles per domain. Examples of lenses (illustrative):

    • Kind-labelled qualified relation record (default A.6.P lens)
    • n‑ary relation with distinguished positions (A.6.5 style)
    • kind‑labelled dependence arrow over a base (A.6.6 style)
    • span/cospan + declared loss/correspondence notes (Bridge‑like relation patterns)
    • correspondence relation + repair operations (sync/consistency relation patterns)

    The lens is a compression device: one stable abstraction that keeps the relation’s arity and polarity stable and makes invariants speakable.

    Last Updated: 2026-06-08 — upstream FPF commit 093d30e8 (github.com/ailev/FPF)