Locally Euclidean Subspace of Euclidean Space is Manifold
Theorem
Let $\R^n$ be an Euclidean space for $n \in \N$.
Let $M = \struct{H, \tau_H}$ be a subspace of $\R^n$, where $H \subseteq \R^n$.
Let $M$ be locally Euclidean of dimension $d$.
Then $M$ is a $d$-manifold.
Proof
From Metric Space is Hausdorff, $\R^n$ is a Hausdorff space.
From Subspace of Hausdorff Space is Hausdorff, $M$ is a Hausdorff space.
From Euclidean Space is Second-Countable, $\R^n$ is second-countable.
From Second-Countability is Hereditary, $M$ is second-countable.
Therefore, $M$ is a $d$-manifold.
$\blacksquare$
Sources
- 2011: John M. Lee: Introduction to Topological Manifolds (2nd ed.) ... (previous) ... (next): $\S 3$: New Spaces From Old: Subspaces. Topological Embeddings