Let $\Omega$ be an open subset of $\mathbb R^n$, with $\Omega \neq \emptyset$ and $\Omega \neq \mathbb R^n$.
Can you give an example where $\partial\Omega \neq \partial\bar{\Omega}$, and how can one exclude this situation?
Let $\Omega$ be an open subset of $\mathbb R^n$, with $\Omega \neq \emptyset$ and $\Omega \neq \mathbb R^n$.
Can you give an example where $\partial\Omega \neq \partial\bar{\Omega}$, and how can one exclude this situation?