Prove or Disprove

John Allen Paulos, from his older volume, “Once Upon a Number”:

“The joke about the mathematics professor who gave a test consisting of four problems is apt. The first three problems required proofs of theorems and the last one was a statement prefaced with the directions ‘prove or disprove.’ One student toiled for a while and then came up to the professor’s desk and asked, ‘On that last problem, do you want me to prove it or disprove it?’ The professor responded, ‘Whichever is the right thing to do.’ ‘Oh,’ replied the student, ‘I can do either one. I was just asking which one you preferred.’ The interchange, of course, would not be a joke if the subject were history or literature.”