Thank you!! I guess in hindsight they did talk about the exponents and the iterated differentiabilty, but I didn't make the connection. I think this was at the

Thank you!! I guess in hindsight they did talk about the exponents and the iterated differentiabilty, but I didn't make the connection. I think this was at the end of the analysis textbook too, in one of those "looking ahead future topics" sections.