| 423 / | HD | CHEMISTRY OF INORGANIC COMPOUNDS |
| 299 | DF | PHOSPHORUS OR COMPOUND THEREOF {5} |
| 304 | DF | .~ Oxygen containing {2} |
| 305 | DF | .~.~ Metal or ammonium containing {5} |
| 307 | | .~.~.~ Hydrogen containing {1} |
| 308 | DF | .~.~.~.~> Orthophosphate (e.g., calcium hydroxyapatite) {1} |