/* another example Prolog knowledge base */

% improved brother rule?

% last modified: 03-3-11

father(athena, zeus). 
father(ares, zeus). 
female(athena). 
male(ares). 
male(zeus). 

brother(Has_brother,Is_brother) :-
   male(Is_brother), 
   father(Has_brother, Father), 
   \+(Is_brother == Has_brother),
   father(Is_brother, Father).