That is my feeling after reading this article. For people who have learned a little bit of Analysis, it is like saying "the earth is round". There is nothing ne

That is my feeling after reading this article. For people who have learned a little bit of Analysis, it is like saying "the earth is round". There is nothing new. The Wikipedia page of Derivative (https://en.wikipedia.org/wiki/Derivative https://en.wikipedia.org/wiki/Derivative) has a detailed description on the linearity. (Well, I do appreciate the author's way of presenting the idea, but I don't think it deserves an in-depth discussion on Hacker News.)