| 558 / | HD | ORGANIC COMPOUNDS -- PART OF THE CLASS 532-570 SERIES |
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| * | DD | ORGANIC COMPOUNDS (Class 532, Subclass 1) {21} |
| 70 | DF | .~ Phosphorus esters (i.e., compounds having the phosphorus ester group, wherein trivalent or pentavalent phosphorus and carbon are bonded directly to the same divalent chalcogen, and wherein the carbon may be single bonded to any atom but may be multiple bonded only to carbon) {18} |
| 73 | DF | .~.~ The phosphorus is in a ring {4} |
| 74 | DF | .~.~.~ Ring phosphorus is shared by two rings {1} |
| 75 |  | .~.~.~.~ Phosphorus and nitrogen in the same ring |