If one is to compute the derivative of
$ y=3x+2 $ by $ \frac{\mathrm{d}(3x+2)}{\mathrm{d} x} $ Would I be working with differential fields? Since differential fields is a first-order theory, but $y$ is a function of $x$ so the derivative function $d$ is a function that takes functions as arguments making it a second-order function.
I must be missing something here...
Thanks