Natura - nature
   actualia - actual entities
     Mundus Plinius - physical world
       naturalia - natural bodies
         "crystal-kingdom"
           chemical substances
             chemical compounds
               Class hydrocarbons [CxHy] - compounds consisting of carbon and hydrogen only
                 Class acetylenes
                   1.1 Class alkynes [CnH2n-2; RC≡CR] - unsaturated acyclic hydrocarbons having one triple bond
                   1.2 Class alkadiynes - unsaturated acyclic hydrocarbons having two triple bonds
                   1.3 Class alkatriynes - unsaturated acyclic hydrocarbons having three triple bonds
                   2 Class cycloalkynes