1. The problem statement, all variables and given/known data I am trying to understand why ℕ the set of natural numbers is considered a Closed Set. 2. Relevant definition A Set S in Rm is closed iff its complement, Sc = Rm - S is open. 3. The attempt at a solution I believe I understand why it is not an Open Set: Given that it includes 0 as a boundary point, it cannot be an open set. As to being Closed. What I am thinking is this: Sc = Rm - ℕ is open because in so doing, we have removed the only boundary point of 0 Therefore, per definition, ℕ or in this case, S is closed. Am I close?