Explanatory notes
… terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium). The heading also covers compounds derived … having the same anion (e.g., rare‑earth metal chlorides), but not mixtures of salts having different anions, whether … are used in nuclear reactors for the absorption of slow neutrons. This heading excludes : (a) Natural compounds …