prove that: S is a subset of R. if every neighborhood of x contains at least one point of S other than x itself, then every neighborhood of x contains infinitely many points of S.
i want to make sure my reasoning is valid. for the => direction, i assume that there exists some neighborhood of x that contains only finitely many points of S. then i say that there exists some neighborhood of x inside this neighborhood such that it contains no points of S other than x by picking it small enough, which is a contradiction.
the <= direction seems clear
also, neighborhoods as defined in this context are the open sets of points "a" such that |x-a| < e for any e.
am i missing any subtleties in my argument? thanks.