## Problem 213 — rank:246

**Title:** Mechanistic origin of seasonality

**Added binding assumptions (LaTeX):**

```latex
Give a stochastic law or sensitivity envelope for $u_t$; an unrestricted residual can absorb any coefficient change and makes attribution vacuous. A perfectly collinear design identifies only coefficient combinations in its observable span. Non-identification of an individual counterfactual contribution follows only when that contribution varies within the resulting equivalence class. Define feasible interventions on correlated predictors rather than impossible isolated historical trajectories.
```

**Direct edits:** 0. **Fresh external checks:** None; supplied sources retained as provenance.