# example Audited Bridge Artifact C: Two Distinct Tight Templates (Non-Tautological Doeblin)

## Overview

RU is a certificate engine for universality and obstructions in constrained nonnegative propagation. Host structures supply finite inputs. Outputs are audited certificates or finite obstruction witnesses.

## What is shipped

| Artifact | Role | Path |
|---|---|---|
| Host model | Two-template tight core with enforced alternation | `sources/ru_bridge/fibonacci_alternation_two_templates_model.json` |
| RU robust certificate | Tight gap, mixed Doeblin word, RC1, rate pack, ε* | `sources/ru/robust_certificate_fibonacci_alternation_two_templates.json` |
| Bridge wrapper | Reduction record pointing to proof carrier | `sources/ru_bridge/bridge_certificate_fibonacci_alternation_two_templates.json` |

## Certified universality facts

- Tight core forces the alternation A_tau → B_pos → A_tau → 
- Doeblin word w=(A_tau,B_pos) has strictly positive product W with δ=1 and U=3.
- Projective diameter bound Δ = 2 log(3), so τ = tanh(Δ/4) = 1/2.
- RC1 holds with gap bound B=0 on the tight core.
- Therefore normalized products contract projectively with an explicit exponential rate (rate_pack).

This is the exact “ posture” you want: a mixed-template core, a mixed-word witness, and an auditable certificate object.

