I've run across stuff in mathematical contexts where they'll throw in a derivative (or other operator) just to get the expression in the form they want. It str

I've run across stuff in mathematical contexts where they'll throw in a derivative (or other operator) just to get the expression in the form they want. It struck me as a bit odd, because hey, where's the change happening? But ultimately it was just a convenience, and maybe it had some underlying meaning in the original context, and maybe it didn't.