3%OWA-open world assumption(incomplete information)
    4%conservative about abnormal definition
    5flies(X):- bird(X), not ab(X).
    6
    7bird(X):- penguin(X).
    8bird(X):- wounded_bird(X).
    9
   10ab(X):- not -penguin(X).  %changed
   11ab(X):- not -wounded_bird(X).  %changed
   12
   13-wounded_bird(X):- -bird(X).  %changed
   14-penguin(X):- -bird(X).  %changed
   15
   16-flies(X):- penguin(X).
   17-flies(X):- -bird(X).
   18
   19%facts
   20bird(tweety).
   21-wounded_bird(tweety).
   22-penguin(tweety).
   23bird(et).
   24-wounded_bird(et).
   25-penguin(et).
   26-flies(et).
   27
   28% penguin(X):-not -penguin(X).
   29% wounded_bird(X):- not -wounded_bird(X).
   30% -bird(X):-not bird(X).
   31
   32#compute 0 {flies(X)}.
   33
   34%?- flies(X).