| 204 / | HD | CHEMISTRY: ELECTRICAL AND WAVE ENERGY |
| * | DD | PROCESSES AND PRODUCTS {7} |
| 157.15 | DF | .~ Processes of treating materials by wave energy {6} |
| 157.6 | DF | .~.~ Process or preparing desired organic product containing at least one atom other than carbon and hydrogen {16} |
| 157.69 | DF | .~.~.~ Heterocyclic product produced {2} |
| 157.71 | | .~.~.~.~ Hetero nitrogen containing {1} |
| 157.72 | DF | .~.~.~.~.~> Hetero nitrogen ring contains at least two hetero atoms |