# example Obstruction Artifact B: Periodic Tight Core (OG1) Witness

## 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 | Strict 2-cycle constraint graph | `sources/ru_bridge/periodic_core_og1_model.json` |
| RU robust certificate (obstruction) | Period-2 tight SCC summary | `sources/ru/robust_certificate_periodic_core_og1.json` |
| Bridge wrapper | Reduction record + obstruction classification | `sources/ru_bridge/bridge_certificate_periodic_core_og1.json` |

## The witness in one line

Tight SCC periods = [2] and aperiodic_scc_count = 0.

This is finite, checkable OG1 structure.

