% The Zebra Puzzle.  There are five houses in a row;  each
% house has associated with it a distinct nationality, pet,
% drink, color, and cigarette.  You are given some clues,
% and the goal is to match up everything.  There is a unique
% solution.

% In this representation, the properties are constants.  For example,
% to express the relationship that the Englishman lives in the Red house,
% one would write England=Red.

set(arithmetic).  % We use this for successor relation.

assign(domain_size, 5).  % The five houses are {0,1,2,3,4}.

list(distinct).      % Objects in each list are distinct.

   [England,Spain,Ukraine,Japan,Norway].          % nationalities are distinct
   [Dog,Snail,Horse,Zebra,Fox].                   % pets are distinct
   [Water,Milk,Juice,Tea,Coffee].                 % drinks are distinct
   [Red,Blue,Yellow,Ivory,Green].                 % colors are distinct
   [Lucky,Winston,Kool,Chesterfield,Parlaiment].  % smokes are distinct

end_of_list.

formulas(assumptions). 

% Definitions of successor and neighbors.

   successor(x,y) <-> x+1 = y.
   neighbors(x,y) <-> successor(x,y) | successor(y,x).

% The clues.

   England = Red.                 Lucky = Juice.            
   Spain = Dog.                   Ukraine = Tea.            
   Norway = 0.                    Japan = Parlaiment.            
   Kool = Yellow.                 neighbors(Kool,Horse).  
   neighbors(Chesterfield,Fox).   Coffee = Green.            
   neighbors(Norway,Blue).        successor(Green,Ivory). 
   Winston = Snail.               Milk = 2.               

end_of_list.