A theorem states that a cat has nine tails. The proof is that no cat has eight tails, and since a cat has one more tail than no cat, it must have nine tails. This is an illogical proof using a play on words to arrive at a mathematically incorrect conclusion for humor or demonstration purposes.

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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.

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