TITLE: Complement is connected iff Connected components are Simply Connected
QUESTION [8 upvotes]: Let $G$ be an open subset of $\mathbb{C}$. Prove that $(\mathbb{C}\cup \{ \infty\})-G$ is connected if and only if every connected component of $G$ is simply connected.

REPLY [5 votes]: If the connected open set $H \subset \mathbb C$ is not simply connected, there is a simple closed curve $C$ in $H$ that is not homotopic to a point in $H$.  Therefore there must be points inside $C$ that is not in $H$.  Such a point and $\infty$ are in different connected components of $({\mathbb C} \cup \{\infty\} - G$.