Natura - nature
   actualia - actual entities
     Mundus Plinius - physical world
       naturalia - natural bodies
         "crystal-kingdom"
           chemical substances
             reactive intermediates
               Class dipolar compounds
                 Class ylides [[RmX+-YRn [<-> RmX=YRn] (X=N,O,P,S,etc.; Y=C, etc.)] or [Z=X+-YRn <-> Z-+X=YRn] or [RmX+-Y <-> RmX=Y]]
                   Class nitrogen ylides [RmN+-CR2]
                     Class nitrile ylides [RC≡N+-CR2 <-> RC-=+N=CR2 <-> RC+=NC-R2 <-> RC:N=CR2]