Facts

• A fact is an expression of the form
  
  $$p.$$
  
  
  where $p$ is an atom
• Its meaning is:
  the proposition (relationship) $p$ always holds
• Example:

  animal(dog).

  likes(cat, fish).

  bigger(men, mice).

• Meaning (under a particular interpretation):

  ``dog'' is an animal

  ``cat'' likes ``fish''

  ``men'' are bigger than ``mice''