| 556 / | HD | ORGANIC COMPOUNDS -- PART OF THE CLASS 532-570 SERIES | 
| * | DD | ORGANIC COMPOUNDS (Class 532, Subclass 1) {3} | 
| 1 | DF | .~ HEAVY METAL CONTAINING (e.g., Ga, In or T1, etc.) {19} | 
| 13 | DF | .~.~ Phosphorus containing {6} | 
| 19 | DF | .~.~.~ Carbon bonded directly to the phosphorus {1} | 
| 20 | DF | .~.~.~.~ Plural carbons bonded directly to the phosphorus {1} | 
| 21 | DF | .~.~.~.~.~ Exactly three carbons bonded directly to the phosphorus (e.g., triphenylphosphines, etc.) {2} | 
| 23 |  | .~.~.~.~.~.~ Hydrogen or halogen bonded directly to the heavy metal |