Stop me if you've heard this one. An infinite number of mathematicians walk into a pub in London. The first one says to the bartender, "I'll have a pint of your finest lager." Second one, "I'll have just half a pint." Third one, "I'll have a quarter of a pint." Bartender raises his hand in a "stop" gesture and says to the whole infinite line, "That's enough-- I'm fetching you the full two pints you're asking for." Calculus in one lesson.