Mathematical Humour

Two operators are walking down the street. One is using the entire street. The other one is in a hurry and asks politely if he may pass. The first one refuses to step aside. The second one gets upset and says: "If you do not step aside quickly, then I will take your derivative". The first one is not impressed and states: "So what, I am e^x". Says the second one: "Yeah, but I am d/dy..."

I did not get it...