geoffhill

  solve(WaterDrinker, ZebraOwner) :-
      % H01: Five houses with positions 1..5.
      Houses = [ house(1, _, norwegian, _, _, _),  % H10: Norwegian lives in the first house.
                 house(2, blue, _, _, _, _),       % H15: Since the Norwegian lives next to the blue house,
                 house(3, _, _, milk, _, _),        %       and house1 is Norwegian, house2 must be blue.
                 house(4, _, _, _, _, _),
                 house(5, _, _, _, _, _) ],
  
      % H02: The Englishman lives in the red house.
      member(house(_, red, englishman, _, _, _), Houses),
      % H03: The Spaniard owns the dog.
      member(house(_, _, spaniard, _, dog, _), Houses),
      % H04: Coffee is drunk in the green house.
      member(house(_, green, _, coffee, _, _), Houses),
      % H05: The Ukrainian drinks tea.
      member(house(_, _, ukrainian, tea, _, _), Houses),
      % H06: The green house is immediately to the right of the ivory house.
      right_of(house(_, green, _, _, _, _), house(_, ivory, _, _, _, _), Houses),
      % H07: The Old Gold smoker owns snails.
      member(house(_, _, _, _, snails, old_gold), Houses),
      % H08: Kools are smoked in the yellow house.
      member(house(_, yellow, _, _, _, kools), Houses),
      % H11: The man who smokes Chesterfields lives in the house next to the man with the fox.
      next_to(house(_, _, _, _, _, chesterfields), house(_, _, _, _, fox, _), Houses),
      % H12: Kools are smoked in a house next to the house where the horse is kept.
      next_to(house(_, _, _, _, horse, _), house(_, _, _, _, _, kools), Houses),
      % H13: The Lucky Strike smoker drinks orange juice.
      member(house(_, _, _, orange_juice, _, lucky_strike), Houses),
      % H14: The Japanese smokes Parliaments.
      member(house(_, _, japanese, _, _, parliaments), Houses),
      % (H09 is built in: Milk is drunk in the middle house, i.e. house3.)
      
      % Finally, find out:
      % Q1: Who drinks water?
      member(house(_, _, WaterDrinker, water, _, _), Houses),
      % Q2: Who owns the zebra?
      member(house(_, _, ZebraOwner, _, zebra, _), Houses).
  
  right_of(Right, Left, Houses) :-
      nextto(Left, Right, Houses).
  
  next_to(X, Y, Houses) :-
      nextto(X, Y, Houses);
      nextto(Y, X, Houses).

   ?- solve(WaterDrinker, ZebraOwner).
   WaterDrinker = norwegian,
   ZebraOwner = japanese .