Einstein riddle

Einstein wrote this riddle early In the 20th century. He said that 98% of the world's population could not solve it. There is no trick, just logic.

In a street, there are 5 houses, each in a different colour.

In each house lives a person with a different nationality.
These five owners drink a certain type of beverage, smoke a certain brand of cigar and keep a certain pet.
No owners have the same pet, smoke the same brand of cigar or drink the same beverage.

The question is: Who owns the fish?

The Brit lives in the red house
The Swede keeps dogs as pets.
The Dane drinks tea
The green house is on the left of the white house
The green house's owner drinks coffee
The person who smokes Pall Mall rears birds
The owner of the yellow house smokes Dunhill
The man living in the center house drinks milk
The Norwegian lives in the first house
The man who smokes Blends lives next to the one who keeps cats
The man who keeps horses lives next to the man who smokes Dunhill
The owner who smokes Bluemaster drinks beer
The German smokes Prince
The Norwegian lives next to the blue house
The man who smokes Blend has a neighbour who drinks water

(Just as a note the poster of this me is one of the 98% in the world. He has NO idea of the answer and would greatly appriecate you /msg sui (answer) and posting it!!!)

Under the assumptions pointed out by rabidcow, below, and using the relations given in the puzzle (re-ordered, for convenience:)

(1) norwegian<-->first
(2) neighbor(norwegian,blue)
(3) red<-->brit
(4) green left of white
(5) yellow<-->dunhill
(6) neighbor (horses, dunhill)
(7) center<-->milk
(8 is arrived at in the deduction)
(9) green<-->coffee
(10) There is no (10).
(11) dane<-->tea
(12) bluemaster<-->beer
(13) neighbor(blends,water)
(14) german<-->prince
(15) pallmall<-->birds
(16) neighbor (blends, cats)
(17) swede<-->dog

 house 1      house 2     house 3         house 4         house 5
 ============|=========|==============|================|===============
 Norwegian(1)       
               blue(2)

(8)                     red/green(3,4) green/white(3,4) white/red(3,4)
 so yellow
 dunhill(5)
               horses(6)                                  
                        milk(7)
                        red (7,8,9)       green          white
                                         coffee(9)
                        Brit (3)
not tea,beer(11,12)
 so water
               Blends(13)
               not beer(12)
               so tea
               Dane(11)
                                                      beer (not needed
                                                      for solution)
                       not Bluemaster(12)
                       not Prince(14)
                       so Pallmall
                       birds(15)

 cats(16)
                                        not Bluemaster(12)
                                          so Prince
                                          German(14)


                                                        must be Swede
                                                        dog(17)
                                          fish.

When we start, we know the following.

The Brit lives in the red house

The Swede keeps dogs as pets.

The Dane drinks tea

The green house is on the left of the white house

The green house's owner drinks coffee

The person who smokes Pall Mall rears birds

The owner of the yellow house smokes Dunhill

The man living in the center house drinks milk

The Norwegian lives in the first house

The man who smokes Blends lives next to the one who keeps cats

The man who keeps horses lives next to the man who smokes Dunhill

The owner who smokes Bluemaster drinks beer

The German smokes Prince

The Norwegian lives next to the blue house

The man who smokes Blend has a neighbour who drinks water

Already we can begin deducing things and forming a table. We know the norwegian is in the first house. We know the middle house, number three, drinks milk, and then we know that the house next to the norwegian, number two, is blue. So if we arrange the table with the norwegian in house number one, and number the rest, you have Norwegian in the first house, second house is blue, third house drinks milk. Make columns for each man's house color, pet, tobacco, and favorite drink.

Now take a break from the table, we'll get back to it later. Now, we're writing up profiles of each of the men, and also profiles of the other facts that aren't associated with any of the men, such as "the owner who smokes bluemaster drinks beer."

The brit is in the red house, so therefore you can rule out yellow, blue, red, green and white. Therefore you know he's not in the first house, because he's not the norwegian, and you know he's not in the second house, which is blue, because we know his house is red. So Brit lives in house three, four or five. What can we rule out about the Brit? We know he does not have a dog, drink tea, or smoke prince. Furthemore, he can't be smoking dunhill because dunhill goes with the yellow house. This leaves him with the smoking options of pall mall, which would mean he keeps birds, or bluemaster which would mean he drinks beer. Now...

We know the Green house is to the left of the white house. These could only be house three and four or four and five, being that we know the second house is blue, and there's only one house to the left of it. Keep in mind the green house drinks coffee, so the green house has to be number four, between the white house and the middle house, which drinks milk. So we assign the color green to house number four. And following that we know house number five is white. We also knew all along that the green house drinks coffee so write that in. Now, since we know that the only two missing colors are house one and three, and that the brit's house is red, he must be in the third house, beause we know the norwegian dude is in the first house. This leaves him, the norwegian, as being the yellow house. We also are given that the yellow house smokes dunhill so write that in. Also, we are given that the horse is next to the guy who smokes dunhill. So the horse is in the second house.

Okay so we know the brit is in the third house so he must be that milk drinker. Elimintating the givens, this leaves him with possibly having fish or birds, and smoking pall mall or bluemaster, but the person who smokes bluemaster drinks beer, so that can't be the brit, because we know he drinks milk. So it must be pall mall, and therefore we know he raises birds.

So now we have all the colors arranged properly, and we know everything about the brit.

Recapping the givens, we see the swede has a dog, so he can't be the second house. Therefore the swede and his dog is either in four or five. The dane drinks tea, so he can't be the fourth house. Therefore, he's in two or five. Right now the german could be any of them, so we'll get back to him.

What about the bluemaster smoker? He drinks beer. This means he's either in house two or five.

More deductions: we know the blends smoker lives next to a cat owner, and lives next to someone who drinks water. These could be the same neighbor or both neighbors on either side. The norwegian smokes dunhill, and house two has horses. So to live next to a cat, the blends smoker would have to be in house two, three, four, or five. Furthermore, the guy drinking water could be in house one, two, or five. So since house five's neighbor drinks coffee, we know that's not it, and that leaves the water drinker with house one or two. So since we've eliminated house five from drinking water, we know house five must be drinking beer and puffing that bluemaster.

Now we know that the water drinker is house one, the norwegian, and the blends smoker is the blue house, number two. Also the blends smoker's neighbor has a cat. This has to be the norwegian.

The only beverage now left (in house two, I hope you're paying attention) is tea, and we know the dane drinks tea. So we have everything on the dane.

Recapping again, we know houses four and five are the swede and the german, but which is which? The Swede has a dog, and the german smokes prince. Ahhhhh, Since the only tobacco left is in four, we know house four is the german, with his prince. And this leaves the dane and his dog in house five. The only slot missing is the german's pet fish.

next_to(X, Y, List) :- iright(X, Y, List).
next_to(X, Y, List) :- iright(Y, X, List).

iright(L, R, [L | [R | _]]).
iright(L, R, [_ | Rest]) :- iright(L, R, Rest).

einstein(Houses, Fish_Owner) :-
  =(Houses, [[house, norwegian, _, _, _, _], _, [house, _, _, _, milk, _], _, _]),
  member([house, brit, _, _, _, red], Houses),
  member([house, swede, dog, _, _, _], Houses),
  member([house, dane, _, _, tea, _], Houses),
  iright([house, _, _, _, _, green], [house, _, _, _, _, white], Houses),
  member([house, _, _, _, coffee, green], Houses),
  member([house, _, bird, pallmall, _, _], Houses),
  member([house, _, _, dunhill, _, yellow], Houses),
  next_to([house, _, _, dunhill, _, _], [house, _, horse, _, _, _], Houses),
  member([house, _, _, _, milk, _], Houses),
  next_to([house, _, _, marlboro, _, _], [house, _, cat, _, _, _], Houses),
  next_to([house, _, _, marlboro, _, _], [house, _, _, _, water, _], Houses),
  member([house, _, _, winfield, beer, _], Houses),
  member([house, german, _, rothmans, _, _], Houses),
  next_to([house, norwegian, _, _, _, _], [house, _, _, _, _, blue], Houses),
  member([house, Fish_Owner, fish, _, _, _], Houses).

Here's the transcript:
[root@somejuan]# pl
% /root/.plrc compiled 0.00 sec, 396 bytes
Welcome to SWI-Prolog (Multi-threaded, Version 5.6.20)
Copyright (c) 1990-2006 University of Amsterdam.
SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software,
and you are welcome to redistribute it under certain conditions.
Please visit http://www.swi-prolog.org for details.

For help, use ?- help(Topic). or ?- apropos(Word).

?- consult('/root/einstein').
% /root/einstein compiled 0.00 sec, 5,208 bytes

Yes
?- einstein(Houses, Fish_Owner).

Houses = [[house, norwegian, cat, dunhill, water, yellow], [house, dane, horse, marlboro, tea, blue],
 [house, brit, bird, pallmall, milk, red]
, [house, german, fish, rothmans, coffee|...], [house, swede, dog, winfield|...]]
Fish_Owner = german