Natura - nature
   actualia - actual entities
     Mundus Plinius - physical world
       naturalia - natural bodies
         "crystal-kingdom"
           chemical substances
             chemical compounds
               Class amides [RkE(=O)l(OH)m (l≠0; ≥1 (OH):=(NR2))]
                 Class primary amides [acyl-NR2]
                   Class lactams [~NRC(=O)[CR2]n~] - cyclic amides of amino carboxylic acids
                     1 Class α-lactams (3 ring atoms)
                     2 Class β-lactams (4 ring atoms)
                     3 Class γ-lactams (5 ring atoms)
                     4 Class δ-lactams (6 ring atoms)
                     5 Class ε-lactams (7 ring atoms)