4. (10 points) Let f : N - R be a real-valued function defined over the set of natural numbers. Either prove that f must be continuous over N or provide an example of a function (from N to R) and a point in its domain (a natural number) such that the function is not continuous at this point. In either case, you must prove your claim using either definition of continuity we covered (see Definition 17.1 and Theorem 17.2)