## Problem 326 — rank:207

**Title:** Origin of oxygenic photosynthesis

**Added binding assumptions (LaTeX):**

```latex
Declare the chronological direction and calibration units for $\tau_O$, and treat $\ell^*$ as a supremum unless attainment is established. A likelihood-tolerance region has coverage only after calibration. The candidate-history bound and functional-feasibility constraints may exclude possible ancestral routes, so distinguish model-imposed from data-supported timing restrictions. Present-day assembly requirements do not establish the order of ancient evolutionary acquisition.
```

**Direct edits:** 1. **Fresh external checks:** None; supplied sources retained as provenance.