"Two Math Professors Are Sitting In A Pub." joke

Two math professors are sitting in a pub.
"Isn't it disgusting", the first one complains, "how little the general public knows about mathematics?"
"Well", his colleague replies, "you're perhaps a bit too pessimistic."
"I don't think so", the first one replies. "And anyhow, I have to go to the washroom now."
He goes off, and the other professor decides to use this opportunity to play a prank on his colleague. He makes a sign to the pretty, blonde waitress to come over.
"When my friend comes back, I'll wave you over to our table, and I'll ask you a question. I would like you to answer: x to the third over three. Can you do that?"
"Sure." The girl giggles and repeats several times: "x to the third over three, x to the third over three, x to the third over three..."
When the first professor comes back from the washroom, his colleague says: "I still think, you're way too pessimistic. I'm sure the waitress knows a lot more about mathematics than you imagine."
He makes her come over and asks her: "Can you tell us what the integral of x squared is?"
She replies: "x to the third over three."
The other professor's mouth drops wide open, and his colleague grins smugly when the waitress adds: "... plus C."