Natura - nature
   actualia - actual entities
     Mundus Plinius - physical world
       Caelum veter. - region of the fixed stars
         (Constellation) Libra veter. - Lib
           (Planetary system) Gliese 581
             1 (Star) Gliese 581
             2 (Planet) Gliese 581 b X. Bonfils et al., 2005
             3 (Planet) Gliese 581 c S. Udry et al., 2007 - "Ymir"
             4 (Planet) Gliese 581 d S. Udry et al., 2007