/* 

  Penguin problem in Picat.

  From Alma-0 program penguin.a0:
  """
  This program shows that it is possible to use Alma-0 for 
  nonmonotonic reasoning.
  We stipulate the following assumptions.

  - The birds which are not abnormal fly
    (i.e., birds usually fly).
  - The penguins are abnormal.
  - Penguins and eagles are birds.
  - Tweety is a penguin and Toto is an eagle.

  The problem is to deduce which of these two birds flies.
  """

  This Picat model was created by Hakan Kjellerstrand, hakank@gmail.com
  See also my Picat page: http://www.hakank.org/picat/

*/


% import util.
% import cp.


main => go.


go =>
  All = findall(B,fly(B)),
  println(All),
  
  nl.

index(-)
penguin(tweety).

index(-)
eagle(toto).

ab(Bird) => penguin(Bird).

bird(Bird) => penguin(Bird); eagle(Bird).

fly(Bird) => bird(Bird), not ab(Bird).