Waiter

Two mathematicians walk into a restaurant for lunch. One challenges the other to a wager, loser pays the tab:

Said the challenger: "The waitperson will not know the correct formula for (a+b)^2."

"You're on!" was the reply.

They place their order and the waitperson is asked the formula for (a+b)^2. The waitperson replied: "Obviously, (a+b)^2 = a^2 + b^2."

"Provided, of course, that a and b are anticommutative!"