Anvari.org

Theorem: A Cat Has Nine Tails. Proof: No Cat Has Eight Tails.

Theorem: a cat has nine tails.

Proof:

No cat has eight tails. A cat has one tail more than no cat.
Therefore, a cat has nine tails.

Related:

Retrieved from http://www.anvari.org/shortjoke/Science_Humor/69_theorem-a-cat-has-nine-tails-proof-no-cat-has-eight-tails.html