Proofs and jokes have a lot in common.
One similarity is their structure. Just as the conclusion of a proof must be justified by the premises, the punch line of a joke must be supported by a series of statements. The following joke provides an example.
- During a flight from Warsaw to New York, members of the flight crew became ill. When the pilot and copilot passed out, flight attendants began asking if anyone on board could fly the plane.
- An elderly Polish gentleman said he had flown supply planes in the army many years ago.
- He was escorted to the cockpit, but upon looking at the controls, he realized that this plane was far more complicated than the ones he had flown years ago.
- He told the flight attendant that he would not be able to fly the plane.
- “I’m sorry,” he said. “I’m just a simple Pole in a complex plane.”
Notice that each statement 1-4 alludes to a different part of the punch line in statement 5. Without any of them, the joke fails. Similarly, a proof with an unsupported conclusion will be invalid.
Another similarity between proofs and jokes is that an elegant proof is as enjoyable as — and perhaps more than — a good joke. My favorite proof, in fact, is one that came to me while I was walking my dog, and its beauty far surpasses that of any anecdote.
Perhaps you don’t buy any of this argument, and that’s fine. But the following five jokes about proofs, taken from Math Jokes 4 Mathy Folks, provide proof that math can be funny. Sort of.
A mathematician was asked, “What is 2 ´ 2?” She thought for a moment, then declared, “I don’t know the answer — but I have a proof that an answer exists!”
At a conference, a mathematician proves a theorem.
Someone in the audience interrupts him. “But, sir, that proof must be wrong. I’ve found a counterexample.”
The speaker replies, “I don’t care — I have another proof for it.”
“Proofs are sooooo boring!” I said.
Thinking quickly, my friend replied, “Well, that’s a given.”
Need More Paper
Did you hear about the one-line proof of Fermat’s Last Theorem?
It’s the same as Andrew Wiles’ proof, but it’s written on a really long strip of paper.
Beyond a Shadow of Doubt
A meek man appeared in a court room, and the judge was incredulous when he read the charges against the man. “Sir,” said the judge, “you’re a well educated man. How did you end up here?”
“I’m a mathematical logician, dealing in the nature of proof.”
“Yes, go on,” said the judge.
“Well, I was at the library, and I found the books I wanted and went to take them out. The librarian told me I had to fill out a form to get a library card, so I filled out the forms and got back in line.”
“And?” said the judge.
“And the librarian asked, ‘Can you prove you’re from New York City?’ So I stabbed her.”