% Constraints satisfaction problem from Albert Einstein's Puzzle
% Author : Feng Di @K.U.Leuven

% Please run this program by ECLiPSe
% ECLiPSe is a constraint processing tool using Prolog

:-lib(ic).

einstein_problem:-
    % I use 5 list of 5 variables
    Nat = [English,Swedes,Danish,Norwegian,German],
    Color = [Red,White,Green,Yellow,Blue],
    Pat = [Dog,Bird,Cat,Horse,Fish],
    Drink = [Tea,Coffee,Milk,Beer,Water],
    Cigarette = [PallMall,Dunhill,Blends,BlueMaster,Prince],

    %domain of variables
    Nat :: 1..5,
    Color :: 1..5,
    Pat :: 1..5,
    Drink :: 1..5,
    Cigarette :: 1..5,

    %constraints
    alldifferent(Nat),
    alldifferent(Color),
    alldifferent(Pat),
    alldifferent(Drink),
    alldifferent(Cigarette),

    English $= Red,
    Swedes $= Dog,
    Danish $= Tea,
    White #= Green+1,
    Green $= Coffee,
    PallMall $= Bird,
    Yellow $= Dunhill,
    Milk $= 3,
    Norwegian $= 1,
    abs(Blends-Cat) $= 1,
    abs(Horse-Dunhill) $= 1,
    BlueMaster $= Beer,
    German $= Prince,
    abs(Norwegian-Blue) $= 1,
    abs(Blends-Water) $=1,

    %search
    flatten([Nat,Color,Pat,Drink,Cigarette],List),
    labeling(List),

    %print solution
    NatNames = [English-english,Swedes-swedes,Danish-danish,Norwegian-norwegian,German-german],
    memberchk(Fish-FishNat,NatNames),
    write('The '),write(FishNat),write(' owns fish.'),nl.