Theorem 26.6. Let f : X → Y be a bijective continuous function. If X is compact and Y is Hausdorff, then f is a homeomorphism. Proof. We shall prove that images of closed sets of X under f are closed in Y; this will prove continuity of the map f^-1. If A is closed in X, then A is compact, by Theorem 26.2. Therefore, by the theorem just proved, f(A) is compact. Since Y is Hausdorff, f(A) is closed in Y, by Theorem 26.3.