How to solve this equation?

[polymath257]

Sure. And there are various levels of math joke, from the mathematical spy that was caught because he was told the sine and didn't know the cosine. But that's off on a tangent.

Then there are the snakes on Noah's arc that didn't go forth to multiply be cause they were adders. But later, they had kids beside a fallen tree: adders can multiply by logs.

Then there is the proof that all horses are the same color (by induction). And the proof (like that above for dogs) that horses have at least 12 legs, which gives a horse of a different color, a contradiction.

The horse proof, of course, fails P(1) -> P(2).  Also, we have the 0 = 1 proof courtesy division by zero.

Or that 1=2 by rearranging the alternating harmonic series. Or by a suitable integration by parts, forgetting the constant.