Open subset of $\mathbb{R}^n$ is not homeomorphic to it

[tymmym]

mathphysics/LeeJM/01smoothmanifolds.tex

Line 33 in c384997

open subset $\mathcal{O} \subseteq \mathbb{R}^n$ homeomorphic to open ball and $\mathcal{O}$ homeomorphic is $\mathbb{R}^n$ since $\mathbb{R}^n$ homeomorphic to open ball.