Uni Göttingen
Institute for Informatics
Databases and Information Systems


Reasoning: Einstein's Puzzle/Fish Puzzle

The below puzzle is known as the "Einstein's Puzzle" of "Fish Puzzle". The reason why it is mentioned here is that at the end of the courses you should be able to write a characterization in Datalog/smodels and in OWL that can be used to ask a reasoner for the solution.

Try first to find a solution on your own (no, not by google). Keep track what knowledge you (often implicitly) use for your conclusions. Encoding this knowledge (not the conclusions themselves) in Datalog or OWL will then allow the reasoner to find the solution.

The Puzzle:

There are five houses in five different colours in a row, starting from left to right. In each house lives a person of a different nationality. These owners all drink a certain type of beverage, smoke a certain brand of cigarette and keep a certain type of pet. No two owners have the same pet, smoke the same brand or drink the same beverage.


  1. The Brit lives in the red house.
  2. The Swede keeps dogs as pets.
  3. The Dane drinks tea.
  4. The green house is directly on the left of the white house.
  5. The green house's owner drinks coffee.
  6. The person who smokes Pall Mall rears birds.
  7. The owner of the yellow house smokes Dunhill.
  8. The man living in the centre house drinks milk.
  9. The Norwegian lives in the first house.
  10. The person who smokes Marlboro lives next to the one who keeps cats.
  11. The person who keeps horses lives next to the person who smokes Dunhill.
  12. The person who smokes Winfield drinks beer.
  13. The German smokes Rothmans.
  14. The Norwegian lives next to the blue house.
  15. The person who smokes Marlboro has a neigbor who drinks water.

The question is: WHO OWNS THE FISH???