Haha that's a good one, I'll need to remember that one. By brain had to do a lap before I could do that one.Hurkyl said:I've heard an interesting story related to this.
A professor wanted to emphasize to his calculus students that using "f" for a function and "x" for real number was merely conventional, and to shock them, he proceeded to write down this definition:
x(f) := f^2
And then work out its derivative, dx/df.
As it so happened, the professor was so confused that he had difficulty working out this simple derivative!!!