Natura - nature
   actualia - actual entities
     Mundus Plinius - physical world
       naturalia - natural bodies
         "crystal-kingdom"
           chemical substances
             chemical compounds
               Class hydrazides [RkE(=O)l(OH)m (l≠0; ≥1 (OH):=(=NRNR2))]
                 Class phosphonic dihydrazides [RP(=O)(NHNH2)2]