this is my code currently, I am trying to solve the zebra puzzle.
exists(A,(A,_,_,_,_)). exists(A,(_,A,_,_,_)). exists(A,(_,_,A,_,_)). exists(A,(_,_,_,A,_)). exists(A,(_,_,_,_,A)). rightOf(A,B,(B,A,_,_,_)). rightOf(A,B,(_,B,A,_,_)). rightOf(A,B,(_,_,B,A,_)). rightOf(A,B,(_,_,_,B,A)). middleHouse(A,(_,_,A,_,_)). firstHouse(A,(A,_,_,_,_)). nextTo(A,B,(B,A,_,_,_)). nextTo(A,B,(_,B,A,_,_)). nextTo(A,B,(_,_,B,A,_)). nextTo(A,B,(_,_,_,B,A)). nextTo(A,B,(A,B,_,_,_)). nextTo(A,B,(_,A,B,_,_)). nextTo(A,B,(_,_,A,B,_)). nextTo(A,B,(_,_,_,A,B)). :- Houses = (house(N1,P1,S1,D1,C1),house(N2,P2,S2,D2,C2),house(N3,P3,S3,D3,C3),house(N4,P4,S4,D4,C4),house(N5,P5,S5,D5,C5)), exists(house(english,_,_,_,red),Houses), exists(house(spainish,dog,_,_,_),Houses), exists(house(_,_,_,coffee,green),Houses), exists(house(ukrainian,_,_,tea,_),Houses), rightOf(house(_,_,_,_,green),house(_,_,_,_,ivory),Houses), exists(house(_,dog,oldgold,_,_),Houses), exists(house(_,_,kools,_,yellow),Houses), middleHouse(house(_,_,_,milk,_),Houses), firstHouse(house(norwegian,_,_,_,_),Houses), nextTo(house(_,_,chesterfields,_,_),house(_,fox,_,_,_),Houses), nextTo(house(_,_,kools,_,_),house(_,horse,_,_,_),Houses), exists(house(_,_,luckystike,orangejuice,_),Houses), exists(house(japanise,_,parliments,_,_),Houses), nextTo(house(norwegian,_,_,_,_),house(_,_,_,_,blue),Houses), exists(house(WaterDrinker,_,_,water,_),Houses), exists(house(ZebraOwner,zebra,_,_,_),Houses). I have typed this up and saved it as zebra.pl, this I open it and enter [zebra] into SWI-prolog, it returns a warning message about the singleton use of N1,P1,C1 etc.. and returns true, then i ask it to print water drinker using print(WaterDrinker) and it returns _G317 and true,
why is it doing this and not returning the answer which could be norwegian, it does the same if i ask it return any variable like C3 or ZebraOwner
