1% false.
    2bird(tux).
    3penguin(tux).
    4bird(tweety).
    5chicken(tweety).
    6
    7flies(tux) :- bird(tux), not -flies(tux).
    8
    9-flies(tux) :- bird(tux), not flies(tux).
   10-flies(tux) :- penguin(tux).
   11
   12flies(tweety) :- bird(tweety), not -flies(tweety).
   13
   14-flies(tweety) :- bird(tweety), not flies(tweety).
   15-flies(tweety) :- penguin(tweety).
   16
   17:- flies(tux), -flies(tux).   18:- flies(tweety), -flies(tweety).   19
   20flies(tux)