In the land of calculus, derivatives often like to keep their functions as pets. All of the derivatives for a function over an interval live together as a derivative family. Unfortunately, their pet function has a problem: it keeps growing and growing and eating all the food in the derivative household.
Concerned, the derivatives take their pet function to the vet to see what is wrong. When the vet asks what’s wrong with the function, the derivatives descibe in detail how their function will not stop increasing.
“This is serious,” replies the vet sternly. “Before we go any further, are you sure that your function is increasing?”
The derivatives reply, “We’re positive.”
This was anonymously posted outside my office door one day.