Define a function such that
Ok, so let's assume we have the function f(x).
If we want to find the derivative, we write f'(x). If we want to find the derivative of this as well, we write f''(x), right?
Now, let's go back to f(x). If we want to integrate this, we write F(x). Now, if we want to integrate F(x) again, how do we write this?