big(bear).
big(elephant).
big(lion).
small(cat).
small(dolphin).
small(monkey).

brown(bear).
brown(monkey).
black(cat).
gray(elephant).
blue(dolphin).
orange(lion).

dark(Z) :- black(Z).
dark(Z) :- brown(Z).

friendof(monkey, cat).
friendof(cat, dolphin).
friendof(monkey, lion).
friendof(bear, elephant).
friendof(lion, bear).
friendof(elephant, bear).
friendof(elephant, monkey).