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Lewis Caroll-ism


  1. The only animals in this house are cats.
  2. Every animal is suitable for a pet, that loves to gaze at the moon.
  3. When I detest an animal, I avoid it.
  4. No animals are carnivorous, unless they prowl at night.
  5. No cat fails to kill mice.
  6. No animals ever take to me, except what are in this house.
  7. Kangaroos are not suitable for pets.
  8. None but carnivors kill mice.
  9. I detest animals that do not take to me.
  10. Animals that prowl at night always love to gaze at the moon.
PROVE: I always avoid a kangaroo.


Source: George Spencer-Brown , Law of Form, pp. 122-23

Hint: Put each of the statement's givens etc. in "if-then" format....then try to form a logical chain that leads to the conclusion. The "bookends" will be the two terms that appear only once...and everything else plays the role of linking "middle terms."


Solution Commentary: Where are Lewis Carroll or Charles Lutwidge Dodgson when you need their help?

If the need continues, you can find an explanation of the full solution in Carroll's book Symbolic Logic or at this website on Lewis Carroll's Soritices.