Natura - nature
   actualia - actual entities
     Mundus Plinius - physical world
       naturalia - natural bodies
         "crystal-kingdom"
           chemical substances
             chemical compounds
               Class "lipids"
                 Class steroids
                   Class pregnanes
                     Class pregnenes
                       Class pregnenediones
                         [pregn-4-ene-3,20-dione [C21H30O2]] see progesterone [C21H30O2]
                         progesterone [C21H30O2]