if_then(['it has hair'],'it is mammal').
if_then(['it gives milk'],'it is mammal').
if_then(['it is mammal','it is tawny','it is carnivore','it has dark spots'],
   'it is a cheetah').
if_then(['it is mammal','it is tawny','it is carnivore','it has black stripes'],
   'it is a tiger').