The first goes off to the toilets, and in his absence his companion calls over the waitress. He tells her that in a few minutes, after his friend has returned, he will call her over and ask her a question. Yes, that's right, he says. The first guy returns and the second proposes a bet to prove his point that most people do know something about basic maths. He says he will ask the blonde waitress an integral, and the first laughingly agrees.
All horses are the same colour.
It is immediate that all horses in a set containing only one horse are the same colour. Remove one horse from the set, so that you have k horses. The inductive hypothesis tells us that all these horses are the same colour. Now return the horse you removed and take out a different horse. Again, by the inductive hypothesis, the remaining k horses are all the same colour.