Topological disc
= Topological disc
{title2=$D^n$}
= Disc
{synonym}
An $n$-dimensional topological disc is a space homeomorphic to a Euclidean ball in $\mathbb R^n$, with its open or closed convention specified. A <closed disc> is homeomorphic to $D^n=\{x\in\mathbb R^n:|x|\leq1\}$. The planar <disk> is the Euclidean two-dimensional instance, rather than the whole abstract topological class.