Clauses

• A clause is a construction of the form
  
  $$p \leftarrow b_1, \ldots, b_n.$$
  
  

• Each of $p, b_1, \ldots, b_n$ are atoms
• Can be read as: $p$ is true if $b_1, \ldots, b_n$ are all true
• $p$ is termed as the head, and $b_1, \ldots, b_n$ as the body
• For convenience, $\leftarrow$ is often written as :-
• Example:

  eats(X, Y):- bigger(X, Y).

  pet(X):- animal(X), sound(X, bark).

• Interpretation:

  The big eat the small, or
  If some X is bigger than some Y, then X eats Y

  A pet is an animal which barks, or
  If X is and animal and X barks, then X is a pet, or
  For X to be a pet, it must be an animal and the sound it produces must be a bark