e
x and a constant are walking down the street. They turn into a dark alley, and a derivative operator jumps out of the shadows and blocks their path.
"Oh no," says the constant, "He's going to turn me into nothing!"
"It's okay," says ex, "I'm ex and I'm not afraid of derivative operators. They can't harm me."
So, ex walks down the alley and greets the derivative operator, "Hi, I'm ex."
And the derivative operator replies, "Hi, I'm d/dy."
(Click here for a nifty flash animation. Thanks Colin!)